Thursday
July 28, 2016

Posts by Reiny

Total # Posts: 35,358

Math
First of all, where does the first line come from? if it is true, then 7(a+b)-5(a+b)=7c-5c 2(a+b) = 2c a+b = c a+b-c = 0 so in your second last line you divided by zero, which is a mathematical No No. any subsequent conclusion you draw would be bogus.
June 9, 2016

Logic and Reasoning
You have to have brackets for your conjecture to be true 15/20 = 3/4 , then (15-3)/(20-4) = 12/16 = 3/4 18/15 = 6/5, then (18-6)/(15-5) = 12/10 = 6/5 suppose a fraction a/b is not in lowest terms and can be reduced to c/d then a/b = c/d = k is (a-c)/(b-d) = k ?? from c/d = k, ...
June 9, 2016

trigonometry
ahh, the old "missing bracket" trap. Thanks Steve.
June 8, 2016

trigonometry
I will write it as: (cosx + cosy)² + (sinx + siny)² = 4cot(x-y/2) --> easier to type LS = cos^2 x + 2cosxcosy + cos^2 y + sin^2 x + 2sinxsiny + sin^2 x = sin^2 x + cos^2 x + sin^ y + cos^2 y + 2(cosxcosy + sinxsiny) = 2 + 2cos(x - y) = 2(1 + cos(x-y) ) RS = 4 cot(...
June 8, 2016

Math
You should know that the volume of a cone = (1/3)π r^2 h Just plug in your data
June 8, 2016

Math
No algebra or variables needed here. Just do the arithmetic. "Harry has $120. Harry has 3 times as much money as Tom" ---> so Tom has $40 "Tom has twice as much money as Gabi" ----> Gabi has $20
June 8, 2016

statistics
z-score = ( X - mean)/sd z-score = (95-80)/10 = 1.5
June 8, 2016

Math
The last part of the sentence " if it is known that tails occurs at least twice?" contradicts the first part. ignoring that last part we would have: C(4,3)(1/2)^3 (1/2) = 4 (1/16) = 1/4
June 8, 2016

Trigonometry
Did you make your sketch? You have a triangle with all sides known, a clear case of the cosine law, let the angle between them be Ø 189^2 = 244^2 + 168^2 - 2(244)(168)cosØ 2(244)(168)cosØ = 244^2 + 168^2 - 189^2 cosØ = (244^2 + 168^2 - 189^2)/(2(244...
June 8, 2016

math
let n be the number he originally bought cost = 20(n/50) = 2n/5 number he sold = n-30 return = 1.2(n-30) profit equation: 1.2(n-30) - 2n/5 = 84 1.2n - 36 - 2n/5 = 84 1.2n - .4n = 120 .8n = 120 n = 150 he bought 150 tomatoes check: cost to buy them = 20(150/50) = $60 return = 1...
June 8, 2016

Math
3n - 12 = 30 3n = 42 n = 42/3 or 14 years
June 8, 2016

Math
no, look at how "an apple is 10% lighter ..." became .9 so what percentage do I need to have .8333... ?
June 8, 2016

Math
g = 1.08 o -----> o = g/1.08 a = .9 o ---> o = a/.9 g/1.08 = a/.9 .9 g = 1.08a a = (.9/1.08) g a = .8333... g state your conclusion.
June 8, 2016

Math
What changes do you think you have to make in my solution? http://www.jiskha.com/display.cgi?id=1465418863
June 8, 2016

Pre-Calculus Matrix
never mind the matrix stuff. Suppose we subtract #3 - #1 I get x + 4y + 6z = 8 but #2 says: x + 4y + 6z = -32 which contradicts the above, so .... no solution
June 8, 2016

Math
yes
June 8, 2016

Math
how did you get that? Are we including the area of the base ?
June 8, 2016

math
if you want the eastward displacement ... x/50 = cos 10° x = .....
June 8, 2016

Math
I think you missed my point. I was pointing out that there is no octagon possible with sides of 19 and apothem of 16. Carefully read what my explanation said. Thus, none of the answers make any sense. Please let your teacher know, so he/she can correct the worksheet. Just ...
June 8, 2016

Math
There is a problem with your question. You said it was a regular octagon with sides 19 inches, forget the apothem part right now. Then you have 8 equal isosceles triangles with an angle of 360/8 or 45° at the top and angles of 67.5° at each of the bases. The height of ...
June 8, 2016

Math
in general if the centre is (h,k), the equation is (x-h)^2 + (y-k)^2 = r^2 notice that the sign inside the bracket is opposite to the sign used in the given point. so for (-4,-3) it must be (x-(-4) )^2 + (y - (-3) )^2 = r^2 (x+4)^2 + (y+3)^2 = r^2 to find the r^2, just plug in...
June 8, 2016

Algebra
Without brackets, your question and your answer is ambigious. I will assume you want cuberoot(3√540 r^3 s^2 t^9) = (3√540r^3 r^3 s^2 t^9)^(1/3) = [3√((36)(15) r^3 s^2 (t^3)^3]^(1/3) = [ 18√15 r^3 s^2 (t^3)^3]^(1/3) = (18√15)^(1/3) r s^(2/3) t^3 ...
June 8, 2016

math
What is C(8,2) x C(9,3) ?
June 8, 2016

Math, Year 10, Simult. Equations
Equations need an "equal" sign and usually consist of both x and y terms. Did you mean y = -x^2 + 3x + 4 and y = x-4 ? Make a table of values for each one. The first one is a downwards opening parabola, get about 4 or 5 points and you should see the general shape of ...
June 8, 2016

Pre-Calculus
agree with 1 1 1 -5 1 -1 3 -1 4 1 1 -2 -----> you had an extra 1 in there 1 1 1 -5 0 2 -2 -4 #1 - #2 0 3 3 -18 1 1 1 -5 0 1 -1 -2 #2 divided by 2 0 1 1 -6 #3 divided by 3 1 1 1 -5 0 1 -1 -2 0 0 -2 4 #2 - #3 1 1 1 -5 0 1 -1 -2 0 0 1 -2 from #3: z = -2 in #2: y - z = -2 y + 2...
June 7, 2016

math
h = -16t^2 + 60t + 3 at ground level , h = 0 16t^2 - 60t - 3 = 0 t = (60 ± √3792)/32 t = 3.799.. or t = a negative it will take appr 3.8 seconds to hit the ground
June 7, 2016

Math (Polar to Cartesian Equation)
in your repertoire of relations in this topic you should have: x = rcosØ and y = rsinØ, and r^2 = x^2 + y^2 then r/x = sec‚ and r/y = cscØ so let's just substitute r^2 = (4r/x)(r/y) r^2 = 4r^2 /(xy) 1 = 4/(xy) xy = 4
June 7, 2016

Math
LS ---> left side RS ---> ???
June 7, 2016

Math
LS = 1/(siny - 1) - 1/(siny + 1) using a common denominator: = (siny + 1 - (siny - 1)/( sin^2 y - 1) = 2/(-cos^2 y) = - 2 sec^2 y = RS
June 7, 2016

math
let their lengths be 3x, 4x, and 2x 3x+4x+2x = 72 solve for x, then sub back into my definitions
June 7, 2016

Math
I strongly suggest that you memorize the 1 , √3, 2 <------> 30-60-90° triangle. You will meet it again and again if you continue to study math
June 7, 2016

Math
sketch a right-angled triangle with angles 30-60-90 label the sides 1 , √3 and 2, with 1 opposite the 30°, etc so 2 --- x 3.5 -----> 7 and 1 -- x 3.5 -----> 3.5 or 7/2 and √3 -----------> 7√3/2 perimeter = 7 + 7/2 + 7√3/2 = 21/2 + (7/2)&#...
June 7, 2016

Math
quite simple really. since angle A = 90° and angle B = 45°, then the other angle is also 45°, and the triangle is isosceles, thus the other two sides are equal. let each side be x x^2 + x^2 = 17^2 2x^2 = 289 x^2 = 289/2 x = 17/√2 = 17/√2 * √2/&#...
June 7, 2016

maths
direct translation of the English to Math: x + x^2 = 1.5|x^2 - x| case1: times 2 2x + 2x^2 = 3x^2 - 3x x^2 - 5x = 0 x(x-5) = 0 x = 0 or x = 5 or case2: x+x^2 = 1.5(x-x^2) times 2 2x + 2x^2 = 3x - 3x^2 5x^2 - x = 0 x(5x-1) = 0 x = 0 or x = 1/5 so x = 0 , (the trivial case) or x...
June 7, 2016

Math
wage = 2500 + .07s , where s is sales
June 7, 2016

Math
Thank you Steve.
June 6, 2016

Math
so your debt would have grown to ... 4300(1.018)^15 = 5619.38 don't you love those "no payments for 2 years deals" ? They always forget to tell you there is still interest involved.
June 6, 2016

Pre cal
no, your equation doesn't even contain any variables. x(7000) + (x+.03)(13000) = 1190 7000x + 13000x + 390 = 1190 20000x = 800 x = .04 or 4%
June 6, 2016

Math
At point A, sketch in horizontals and verticals the angle between AC and the x-axis is 35° , (305° - 270°) So at A by alternate angles and parallel lines the angle between AC and the horizontal is 35° And AB divides the right angle at A into angles of 64°...
June 6, 2016

French Check Ms. Sue
number 9 is poorly worded The way of writing time in ascending order of day/month/year is standard in most of the world, including France, Canada, and English speaking countries, with the exception of the US.
June 6, 2016

algebra
At off peak rate: cost = .85t at peak time rate: cost = 1.2t I can't do the graphs for you, but I suggest for the first you use: (0,0) and (20, 17) to sketch the first graph, and (0,0) and (20, 24) for the second one sub t = 8 into off-peak equation and into the peak ...
June 6, 2016

Algebra
Strange to ask for an "estimate" for a solution to an equation that can be done mentally. n = -1/6 no idea what you mean by "use a table".
June 6, 2016

math
33 1/3% = 100/300 = 1/3 as a fraction or .333.... as a decimal (the 3 should be shown to be repeating) your decimal of .33 would be 33 % , not 33 1/3 % 78% of 20 = appr 80% of 20 = appr 16
June 6, 2016

math
for ii) I was thinking: prob(same gender) = Prob(both males) or prob(both female) = (2/3)^2 + (1/3)^2 = 4/9 + 1/9 = 5/9 prob(different gender) = 1 - 5/9 = 4/9 or Prob(male, female) or Prob(female, male) = (1/3)(2/3) + (2/3)(1/3) = 4/9
June 6, 2016

geometry
Check what you typed, how it came out, and if it makes sense to you.
June 6, 2016

Math :(
1. correct if you reduce it to 7/36 2. prob(2whites) = (2/9)(1/8) = 1/36 3. prob(2 purples) = (7/9)(6/8) = 7/12 so what do you think when comparing 1/36 with 7/12 ?
June 6, 2016

maths
number in lot A ---- x number in lot b ---- y (2/3)x + y = 400 times 3 2x + 3y = 1200 ** x + (4/5)y = 460 times 5 5x + 4y = 2300 *** ** times 4 : ---> 8x + 12y = 4800 *** times 3: --> 15x + 12y = 6900 subtract them: 7x = 2100 x = 300 in ** 600 + 3y = 1200 y = 200 total ...
June 6, 2016

Algebra
The way you typed it, it would become x = 2y/2 * y + 5 somehow I don't think you meant that. If you meant: x = 2y/(2y) + 5, the 2y would cancel and the statement would be false If you meant: x = 2y/(2y+5) cross-multiply ... 2xy + 5x = 2y 2xy - 2y = -5x y(2x - 2) = -5x y...
June 6, 2016

Algebra
Did you substitute each one to see ? How about the last one? for (5,2) is 2 = 5-3 ??
June 6, 2016

Maths
tanØ = 3/4 = y/x so x=4 and y=3 OR x = -4, y = -3 r^2 = x^2 + y^2 = 25 r = 5 cos^2 Ø - sin^2 Ø = (4/5)^2 - (3/5)^2 = 16/25 - 9/25 = 7/25
June 6, 2016

MATHS
Whatever "d/f coes" are, the must look like ABxxx, where x is one of the given digits. I will assume that repetition is allowed. no. of ways = (1)(10)(10)(10) = 1000
June 6, 2016

algebra
So the foot of the ladder is 10 ft from the building. and you want to reach a height of 13 ft L^2 = 13^2 + 10^2 = 269 L = √269 = appr 16.4 m Why do we have to know the fence is 9 ft high? Am I missing something?
June 5, 2016

Math (Right Triangle Trig)
Make a sketch in your notes regarding CAST It tells you in which quadrants the main trig ratios of (S)ine, (C)osine and (T)angent are positive. Of course if the cosine is positive then its reciprocal, the secant, is also positive, etc since tanØ = 5/7 = y/x x = -7 , y...
June 5, 2016

Math
let the distance be d and the first rate be t original time = d/t new rate = .8t new time = d/.8t = 1.25 d/t so the time increased by 25%
June 5, 2016

@ Ritobroto - math
Always check your answers before you post them. from my equation: x + x+9 + 3x = 89 5x = 80 x = 16 according to my definitions: first = 25 second = 16 third = 48 Is their sum equal to 89 ? , YES Do they fit the given conditions ?, YES Yours do not fit the original conditions ...
June 5, 2016

math
second --- x first ---- x+9 third ---- 3x x + x+9 + 3x = 89 carry on
June 5, 2016

Algebra I
e.g. √245 = x first guess: x = 15 245/15 = 16.33333 average with previous guess: (15+16.33333..)/2 = 15.6666.. <---- new guess 245/15.6666.. = 15.63829.. average with previous guess: (15.6666.. + 15.63829..)/2 = 15.65248... 245/15.65248 = 15.65246... average with ...
June 5, 2016

Algebra 2
let the 3 cosecutive odd numbers be x-2 , x, and x+2 3(x-2 + x + x+2) = x(x-2) - 152 9x = x^2 - 2x - 152 x^2 - 11x - 152 = 0 (x-19)(x + 8) = 0 x = 19, or x = -8 , but x is to be positive the 3 numbers are: 17, 19, and 21 check: their sum = 57 3 times their sum = 171 product of...
June 5, 2016

Math
let her sales be s .15s + 3000 ≥ 4200
June 5, 2016

Algebra 2
Did (0,5) and (5,0) satisfy both equations when you substituted ? If so then you are correct.
June 5, 2016

Math-SineLaw
You are right, you have to use the sine law Since you know 2 angles, we can find the angle at F to be 51.2° So AF/sin87.3 = 34.32/sin51.2 AF = 34.32sin87.3/sin51.2 calculator time ..... AF = 43.988... repeat similar steps to find BF
June 5, 2016

Math
LS = 1 + (e^(2x) - 2e^0 + e^(-2x) )/4 = (4 + e^(2x) - 2 + e^(-2x) )/4 = ( e^(2x) + 2e^0 + e^(-2x) )/4 = ( (e^x + e^-x)/2 )^2 = RS
June 5, 2016

Math
What elements do you see in U which are NOT in T ?
June 5, 2016

math
1 litre = 10^3 cm^3 or 1000 cm^3 10 litres = 10,000 cm^3 I will assume your tank is 80 cm by 60 cm by 50 cm, and not 0.6 and 0.5 cm like you typed volume = 80(60)(50) cm^3 = 240000 cm^3 time for the given rate = 240000/10000 seconds = 24 seconds
June 5, 2016

Math w/reply
Thanks Bob for clearing that up. I was curious and checked some of my bottles of Tylenol etc, none of them up here in Canada have units such as grains, it is all in mg.
June 5, 2016

maths
"unit digit is 4" ----> X4 "tens digit is multiple of 3" ---> 34, 64, 94 "sum of digits is odd" ---> 34 or 94
June 5, 2016

Math(Revised)
Make a sketch, with P for Phoebe and T for Tucker as a horizontal line, so that PT = 45 m Let B be the position of the balloon, so that angle BPT = 43° and angle BTP = 31° Let AB be the height of the balloon with A directly below B on PT sin 43° = AB/BP ---> BP...
June 4, 2016

math
basic right-angled triangle trig let the height be h ft sin 70 = h/32 continue ....
June 4, 2016

Math
How did you possible get those answers? You are dealing with the simple metric system, so everything is simply multiplying or dividing by multiples of 10, the significant digits don't change. 1 g = 1000 mg so (1/100) g = (1/100)(1000) mg = 10 mg #2 1 mg = (1/1000) g so .3 ...
June 4, 2016

math
just test them, of course the largest number would the potential hypotenuse. e.g. c) is 28^2 + 45^2 = 53^2 ?? LS = 784 + 2025 = 2809 RS = 2809 Looks like we have a winner. Do the same for the others, there may be more
June 4, 2016

Algebra
I am sure you meant: 2x/(x-5) + 1/(x-1) = 0 multiply each of the three terms by (x-5)(x-1) , the LCD 2x(x-1) + 1(x-5) = 0 2x^2 - 2x + x - 5 = 0 2x^2 - x - 5 = 0 x = (1 ± √41)/4 the way you have it, it would be 2 - 5 + 1/x - 1 0 1/x = 4 x = 1/4
June 4, 2016

Algebra
by the looks of this, I bet you meant: x/(x-4) - 4/(x-5)=- 4/(x^-9x +20) x/(x-4) - 4(x-5) = 4/( (x-4)(x-5) ) Major hint: what would happen if I multiplied each of the three terms by (x-4)(x-5) ?? Give it a try, it becomes very easy.
June 4, 2016

maths
weight of water when full --- x kg weight of empty tank ------- y kg (1/2)x + y = 310 ** (3/4)x + y = 450 *** subtract: *** - ** (1/4)x = 140 x = 560 back in ** 280 + y =310 y = 30 the tank weighs 30 kg
June 4, 2016

math
full capacity ---- x litres (5/7)x - 440 = (2/5)x multiply by 35 , the LCD 25x - 15400 = 14x take over
June 4, 2016

math
Wow, a 100 ft ladder ???? And the base is 40 ft out ??? totally totally unsafe , absurd and against all safety regulations.
June 3, 2016

Math
prob(win) = 1/1000 Expected value = (1/1000)($800) = $.80 which would a "fair" price for the ticket.
June 3, 2016

Math
The period is π , and the amplitude is 7 so we could go with y = 7sin πt we want the min to be 0 and the max to be 14 so we need y = 7sin πt + 7 when t = 0 we want y = 0, so we need a phase shift y = 7sin π(t+Ø) + 7 when t=0, we want y = 0 when t = 1...
June 3, 2016

Add Math
let the point be P(x,y) so √( (x-1)^2 + (y-6)^2 ) = √( (x-3)^2 + (y-2)^2 ) square both sides, and expand x^2 - 2x + 1 + y^2 - 12y + 36 = x^2 - 6x + 9 + y^2 - 4y + 4 4x - 8y = -24 x - 2y = -6 Notice that this is the equation of the right-bisector of the line joining...
June 2, 2016

Polynomials and properties of exponenets
-3(4x+5) = -12x - 15 which is C 5k^2(-6k-2k+6) = -30k^3 - 10k^3 + 30k^2 which is none of them. I suspect a typo, why would you have two like terms in the bracket ? the others are correct
June 2, 2016

algebra
And here I was under the impression that I had answered this for you. http://www.jiskha.com/display.cgi?id=1464879381 Where you actually given some functions that you did not post?
June 2, 2016

algebra
all kinds of functions. Any 3 non-collinear points can be expressed by a quadratic, a cubic, a trig function .... e.g Wolfram found: y = -4.7632sinx + 8.70749cosx - 7.70749 if you want a quadratic" y = ax^2 + bx + c -7 = 4a - 2b + c 1 = c -17 = 9a + 3b + c solve for a, b...
June 2, 2016

Math
slope = (y2 - y1)/(x2 - x1) sub in your values and evaluate
June 2, 2016

math
original room : x m by y m , area = xy case1: (x+2)(y+3) = xy + 16 xy + 3x + 2y + 6 = xy+16 3x + 2y = 10 case2: (x-1)(y+2) = xy + 16 xy + 2x - y - 2 = xy+16 2x - y = 18 solve: 3x+2y=10 2x -y = 18 I get a negative value for y, which makes no sense check your problem, or your ...
June 2, 2016

Chemistry , not maths
to get the tutor for your question, make sure your subject is correct
June 2, 2016

Simultaneous equation
It is just a matter of translating the English to Math. Going with your definitions of A and B "the sum of their ages" ---> A + B "the difference of their ages" --> A-B "is equal to 5 times" ---> = 5(.... (the sum of their ages) is equal...
June 2, 2016

math
simple method: numbers which divide by 630 leaving remainder of 6: 636 1266 1896 2526 3156 3786 4416 ... numbers which divide by 940 leaving remainder of 4: 944 1884 2824 3764 ...... looks hopeless alternate method Let that number be k then k/630 = x + 6/630 --> k = 630x + ...
June 2, 2016

MAth
What is 200(1.06)^2 - 200 ?
June 1, 2016

Mathematics
False! Counter-example 4 possible multiples of 6 are 6, 12, 30, and 42 their sum is 90 but 90 is not divisible evenly be 12, so the statement is false
June 1, 2016

Math trig
first one is true tan A = sinA/cosA square both sides: tan^2 A = sin^2 A/cos^2 A watch the second one, wouldn't the 2's on the right side cancel for you in your equation?? correct way: since tanA = sinA/cosA so 2(tanA) = 2(sinA/cosA) = 2sinA/cosA
June 1, 2016

math
slope = (.4 + 14)/(4+5) = 14.4/9 = 144/90 = 8/5 so using (-5,-14) y+14 = (8/5)(x+5) 5y + 70 = 8x + 40 8x - 5y = 30
June 1, 2016

Pre-Cal: Plz help!
[(X^(2)+3)^(1/3)](-1)(x^(-2))+[1/3(x^(2)+3)^(-2/3)](2x)(x^(-1)) = [ ( x^2 + 3)^(1/3) ] ( -1/x^2 ) + [ (1/3) /(x^2 + 3)(2/3) ](2x/x) I entered it exactly the way you typed it, and did not get that answer. Check your brackets http://www.wolframalpha.com/input/?i=simplify+%5B(X%...
June 1, 2016

Quadratic Functions2
This question and the other one I just answered for you are fundamental questions that you just have to know how to do in this topic. To simply say, "I can't figure out how to get the answer" tells me you are not even in the course. Anyway.... since you know the ...
June 1, 2016

Quadratic Functions1
1. f(x)= 3(x-2)^2-6 with zeros of 0.59 and 3.41 everything you asked for , except the y-intercept, can simply be stated directly from the equation: x-intercepts, you stated them already axis of symmetry: x-2 = 0 or x = 2 vertex: (2,-6) for the y-intercept, let x = 0 y = 3(-2)^...
June 1, 2016

@ Kaitland and Othilia - Algebra
The purpose of this webpage is not to facilitate cheating. You are in danger of being banned from using it.
June 1, 2016

mathhhhhh plz help immediately
is that X^3=36.31*10^-24 ? if so , just take the cube roots of that number. I get (36.31)^(1/3) * 10^-8 or appr 3.3114 * 10^-8
June 1, 2016

Math- Prob Stat
The absolutely perfect webpage for your question. Just plug in the values http://davidmlane.com/normal.html
June 1, 2016

math plz help ;-;
Is the top of the ice-cream a hemisphere? "On top of the cone is 18 as the bottom is 26. " This makes no sense to me. I need the radius of the cone, and the height of the cone. (The radius of the hemisphere is determined by the radius of the cone)
June 1, 2016

math plz help ;-;
Consider the following properties of a triangle 1. If a triangle has an obtuse angle, that angle must be opposite the largest side 2. A triangle can have at most one obtuse angle 3. If a triangle has sides a, b, and c, with c as the largest side, then if -- c^2 > a^2 + b^2...
June 1, 2016

stats
number of possible 5-digit pins = 3x3x3x3x3 = 243 prob(same) = 1/243
June 1, 2016

math plz help ;-;
slope is (-7-8)/(1+4) = -15/5 = -3 so y = -3x + b plug in one of your points, I picked (-4,8) : 8 = -3(-4) + b ---> b = -4 so y = -3x - 4 now, how easy was that?
June 1, 2016

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