Saturday
January 21, 2017

Posts by Reiny

Total # Posts: 37,341

Calculus
let the edge be x cm long V = x^3 dV/dt = 3x^2 dx/dt = 3x^2 (3) = 9x^2 cm^3/s so when x = 1 dV/dt = 9(1) cm^3/s do the 2nd part in the same way
November 2, 2016

calculus
let the height be h ft then diameter = 3h ft, and the radius is 3h/2 V = (1/3)? r^2 h = (1/3)? (9h^2/4)(h) = (3/4)? h^3 dV/dt = (9/4)? h^2 dh/dt when h = 15, dV/dt = 10 10 = (9/4)? (15) dh/dt dh/dt = 40/(135?) ft/s = 8?/27 ft/s
November 2, 2016

Math, Precalc
3^x + 5^(x+3) - 3^(x+4) + (1/3)5^(x+2)= 0 3^x(1 - 3^4) + 5^(x+2)(5 + (1/3)(1) ) = 0 -80(3^x) + (16/3)(5^(x+2) = 0 times -3/16 15(3^x) - 5^(x+2) = 0 15(3^x) = 5^(x+2) divide by 5 3(3^x) = 5^(x+1) 3^(x+1) = 5^(x+1) this can only be true if x = -1 that is, if 3^0 = 5^0 , which ...
November 2, 2016

Math, Precalc
Sue's time riding the bike = 5/15 hrs = 1/3 hr Sue's time walking the 2 miles = 2/3 hr total time = 2/3 + 1/3 = 1 hr total distance = 7 miles average speed = 7/1 = 7 mph
November 2, 2016

Maths
let the number of sides be n each interior angle = 180(n-2)/n each exterior angle = 360/n 180(n-2)/n < 10(360/n) by 84 180(n-2)/n = 10(360/n) - 84 times n, which is positive 180(n-2) = 3600 - 84n 180n - 360 = 3600 - 84n 264n = 3960 n = 15 sum of angles = 180(15-2)° = ...
November 2, 2016

word problem
48/16 = 3 72/12 = 6 so I can draw 18 rectangles of 12 by 16 on a piece of 48 by 72 BUT, using a regular saw there will be a saw-cut waste and that changes the question. I will assume your question is ignoring the sawdust.
November 1, 2016

Pythagorean theorem
depends on what the question is.
November 1, 2016

Calculus
f''(x) = x^2 f'(0) = 8, f(o)=4 if f''(x) = x^2, then f'(x) = (1/3)x^3 + c for the given: 8 = (1/3)(0) + c ---> c = 8 , and f'(x) = (1/3)x^3 + 8 f(x) = (1/12)x^4 + 8x + k f(0) = 4 4 = (1/12)(0) + 8(0) + k ----> k = 4 f(x) = (1/12)x^4 + 8x + 4 ...
November 1, 2016

Calc
height = -4.9t^2 + 10t + 2 d(height)/dt = -9.8t + 10 = 0 at max height 9.8t = 10 t = 10/9.8 height = -4.9(10/9.8)^2 + 10(10/9.8) + 2 = appr 7.102 m is the max height when it reaches the ground 0 = -4.9t^2 + 10t + 2 4.9t^2 - 10t- 2 = 0 t = (10 ± ?139.2)/9.8 = 1.306 ...
November 1, 2016

math
each side of first one is 848/4 or 212 cm each side of the 2nd is 436/4 or 109 cm so the area of the first = 212^2 cm^2 = 44944 cm^2 the area of the 2nd is 109^2 cm = 11881 cm^2 total area = 56825 cm^2 each side is ?56825 = 5?2273 and the perimeter = 20?2273 = appr 953.52
November 1, 2016

Math
p + pr(12) = 2p p(1 + 12r) = 2p 1 + 12r = 2 12r = 1 r = 1/12 = appr .08333.. or 8 1/3% consider $100 in 12 yrs, at a rate of .083333..., we would have 100 + 100(.08333..)(12) = 200 check!
November 1, 2016

Maths
(3/4) / 2 = 15/x (3/4)x = 30 x = 30(4/3) = 40 or notice: sugar : butter = 3/4 : 2 = 3 : 8 so 15:x = 3:8 3x=120 x=40
November 1, 2016

mathematics
ones digit ---- x tens digit -----x+3 x+x+3=13 x = 5 ----> x+3 = 8 so the number is 85
November 1, 2016

math
let's first handle 75 degrees tan75 = tan(30+45) , skipping the degree symbols = (tan30 + tan45)/(1 - tan30tan45) = (1/sqr3 + 1)/(1 - (1/sqr3)(1)) = (sqr3 + 1)/(sqr3 - 1) tan 75 = 2tan(75/2)/( 1 - tan^2 (75/2) ) let tan(75/2) = x for easier typing (sqr3 + 1)/(sqr3 - 1) = ...
November 1, 2016

math
What is 3(2 1/4) inches = 3(9/4) inches = 27/4 inches or 6 3/4 or 6.75 inches
November 1, 2016

Algebra
We don't "guess" in mathematics. just translate the English to Math: (1/2)m + (1/3)s = 11 times 6, the LCD 3m + 2s = 66 ** 6 years from now: (m+6) + (s+6) = 40 m + s = 28 *** 2 times *** ---> 2m + 2s = 56 subtract from ** m = 10 back in *** 10 + s = 28 s = 18 ...
November 1, 2016

algebra--miss sue
small correction: the in-equation should be (p - .2p) - 50 ≤ 150 or .8p - 50 ≤ 150 check: .8p ≤ 200 p ≤ 200/.8 or p ≤ 250 phone could cost $250 less 20% or less $50 means cost ...
October 31, 2016

math 142
reading past the strange symbols: 1,000 are deposited into an account quarterly for eight years at an interest rate of 7.878 % compounded quarterly. How much is in the account at the end of the 8 years? i = .07878/4 = .019695 n = 32 amount = 1000(1.019695^32 - 1)/.019695 I got...
October 31, 2016

Algebra
number of tens --- x number of fives --- x+4 number of twenties -- 2x-3 now for their value: 10x + 5(x+4) + 20(2x-3) = 290 solve for x, sub back into my definitions
October 31, 2016

Algebra
width --- x length --- 2x+4 x(2x+4) = 286 2x^2 + 4x - 286 = 0 x^2 + 2x - 143 = 0 (x+13)(x-11) = 0 x = 11 or x = -13, the last part is not possible the width is 11, the length is 26 check: 26 is 4 more than twice 11 area = 11(26) = 286
October 31, 2016

algebra
smallest --- x middle ---- x+10 largest ---- 3x x + x+10 + 3x = 180 etc
October 31, 2016

Adv. functions
You should know these identities: sin(Ï€+x) = -sinx e.g. sin 210° = sin(180°+30°) = -sin30° cos(Ï€/2) - x) = sinx e.g. cos(60) = cos(90-30) = sin30 cos(Ï€+x) = -cosx e.g. cos 210° = -cos30° sin(3Ï€/2 + x) = -cosx ...
October 31, 2016

Math
The standard formula amount = paym( (1+i)^n - 1)/i assumes that payments are made at the end of a payment periods, yours are made at the beginning of each period. I will pretend we have 145 payments, but then subtract the last one i = .046/12 = .003833... (I stored in my ...
October 31, 2016

maths
Why did you repost all those questions again, they had all been answered http://www.jiskha.com/display.cgi?id=1477910441
October 31, 2016

maths
http://www.jiskha.com/display.cgi?id=1477910197
October 31, 2016

Maths
http://www.jiskha.com/display.cgi?id=1477909974
October 31, 2016

maths
http://www.jiskha.com/display.cgi?id=1477909541
October 31, 2016

maths
http://www.jiskha.com/display.cgi?id=1477909333
October 31, 2016

math
I read that as: (secØ - tanØ)/(secØ + tanØ) = 1/4 4secØ - 4tanØ = secØ + tanØ 3secØ = 5 tanØ 3/cosØ = 5sinØ/cosØ 5sinØcosØ = 3cosØ 5sinØcosØ - 3cos&...
October 31, 2016

Math
So if there are only two tests, (x+54)/2 = 74 x+54 = 148 x = ..
October 31, 2016

Maths
for any n-gon, the sum of interior angles is 180(n-2) °
October 31, 2016

Maths
Did you make your sketch ? Two concepts are needed here: 1. the slope of perpendicular lines are negative reciprocals of each other 2. You have to know how to find the distance between two points. 1. slope of AB = (9-1)/(3-5) = -4 so slope of AC = + 1/4 but slope of AC = (y-5...
October 31, 2016

maths
One of the most basic concepts in this topic is "finding the slope between two points" Your text and notes MUST contain the steps I will do the first one, you do the rest slope = (y2-y1)/(x2-x1) = (6-5)/(-4-1) = 1/-5 or - 1/5
October 31, 2016

maths
I will do the first one, you do the other two in the same way. Let P(x, y) be on AB so that AP/PB = 1/2 for the x: (x-1)/(-4-x) = 1/2 2x - 2 = -4 - x 3x = -2 x = -2/3 for the y: (y-3)/(-1-y) = 1/2 2y - 6 = -1 - y 3y = 5 y = 5/3 so P is (-2/3 , 5/3) for b), I am sure you meant...
October 31, 2016

MATHS URGENT PLEASE HELP
midpoint between (x1, y1) and (x2, y2) = ( (x1+x2)/2 , (y1 + y2)/2 ) a) so C = ( (4+6)/2 , (-3-2)/2 ) = (5 , -5/2) b) use the method I just showed you in the previous post to find the two length, show them equal.
October 31, 2016

MATHS URGENT PLEASE HELP
Just use your formula Dist = √(x2-x1)^2 + (y2-y1)^2 ) = √( 6-1)^2 + (10-(-5))^2 ) = √(25 + 225) = √ 250) = √25 * √10 = 5√10 Do the 2nd one in the same way
October 31, 2016

intermediate algebra
1. smaller number --- x larger number --- x+8 (1/2)(x+8) + (1/4)x = 22 etc 2. son's age 10 years ago --- x man's age 10 years ago ---- 3x in 12 years, son's age = x+22 in 12 years, man's age = 3x+22 x=22 = (3/5)(3x+22) etc 3. Let job to be done be 1 unit let A...
October 31, 2016

MATH PLEASE HELP!!!
1. (3/4)z + 6 = (3/4)(x + 8) check by expanding 2. 18x + 6y = 6(3x + y)
October 30, 2016

Permutations
In the majority of texts the word "committee" usually denotes combinations, that is there is no specific order. In that case the result would be C(11,3) which is 165 But you titled your post "permutations", so Steve's answer would apply for that ...
October 30, 2016

Math
one rotation = 2πr = 28π inches = 28π/12 or 7π/3 ft or appr 7.33 ft number of rotations to go 440 ft = 440 ÷ (7π/3) = 1320/(7π) or appr 60.024 rotations time at 15 rotations per min = (1320/(7π)) / 15 = 4 minutes
October 29, 2016

math
prob(defect) = 3/12 = 1/4 prob(working) = 3/4 prob (5 of 5 are working) = C(5,5) (3/4)^5 (1/4)^0 = 243/1024 prob(3 work, 2 don't work) = C(5,3)(3/4)^3 (1/4)^2 = 10(27/64)(1/16) = 270/1024
October 29, 2016

math
prob(backup system works) = prob(1 of 2 generators work) + prob(both will work) = C(2,1)(.98)(.02) + C(2,2) (.98)^2 = .9996
October 29, 2016

Maths
Key point: When they pass each other they both will have traveled the same time let the distance covered by the faster car be x km distance covered by slower car = 400 - x km time of faster car = x/90 time of slower car = (400-x)/70 (400-x)/70 = x/90 (400-x)/7 = x/9 7x = 3600...
October 29, 2016

math
This is an AP, where a = 12, and d = 2 sum(6) = (6/2)(24 + 5(2)) , using our formula = 3(34) = 102 or ... if you don't know what an arithmetic sequence is: day1 = 12 day2 = 14 day3 = 16 day4 = 18 day5 = 20 day6 = 22 add them up to get 102
October 29, 2016

PreCal
b = -(4-√3) = (-4 + √3) then b^2 = 16 - 8√3 + 3 = 19 - 8√3 Bob had 15-8√3 for that part modify his solution.
October 28, 2016

macomb
You have no exponents in your original question. Ms Sue's answer is correct for the question you typed. did you mean −8^−1 + 8^−2 ? then = 1/-8 + 1/8^2
October 28, 2016

Algebra
You did not post the sequence
October 28, 2016

math
A = 2 pi r (r+h) A = 2π r^2 + 2πrh A - 2πr^2 = 2πrh h = (A - 2πr^2)/(2πr)
October 28, 2016

math
You probably meant to type: y = (2x^2 - 5)/(3x^2 - 4) ok, what about it?
October 28, 2016

Math
I have no idea how you got .1446.. 12% ---> 0.12 17% ---> 0.17 3% ---> 0.03 add them up to get 0.32
October 28, 2016

Math
area = 4(2/3) ft^2 = 8/3 ft^2
October 28, 2016

Math
Both the first and the third are given in terms of the 2nd, so we will let the second be our base variable let the 2nd be x then the first is 3x and the third is 10x 10x - 3x = 1050 7x = 1050 x = 150 sub back into my definitions and add them up
October 27, 2016

Math
Ms Sue's answer is the correct one.
October 26, 2016

Differential calculus
y=(√e^x)/x y = (e^(x/2) )/x dy/dx = (x(1/2)e^(x/2) - e^(x/2) )/x^2 simplify if needed.
October 26, 2016

Differential calculus
what kind of root? square root ? is it √(e^x/x) or (√e^x) / x ?
October 26, 2016

Differential calculus with analytic geometry
xy^2+4y^3=x-2y x(2y)dy/x + y^2 + 12y^2 dy/dx = 1 - 2dy/dx dy/x(2xy + 12y^2 + 2) = 1 - y^2 dy/dx = (1 - y^2)/(2xy + 12y^2 + 2)
October 26, 2016

Math
Use a Venn diagram, put in all the data values, and your answers can just be read from the diagram
October 26, 2016

Calculus
2x^2y-3y^2=-11 4xy + 2x^2 dy/dx - 6y dy/dx = 0 dy/dx(2x^2 - 6y) = -4xy dy/dx = -4xy/(2x^2 - 6y) at (2,-1) dy/dx = -4(2)(-1)/(8 -6(-1)) = 8/14 = 4/7 equation of tangent: y+1 = (4/7)(x - 2) massage it any way you need to
October 26, 2016

Algrebra
To visualize the different cases, why not give yourself an actual point. e.g. 2) let (x,y) = (-4,5) <---- had to be in quadrant II then (-x,y) = (4,5) , which is in first quadrant (x,-y) = (-4,-5) , in the third (-x,-y) = (4,-5) , in the fourth
October 25, 2016

Algebra
number of tens ---- x number of fives ---- x+2 number of twenties -- 2x-3 value equation: 10x + 5(x+2) + 20(2x-3) = 445 10x + 5x + 10 + 40x - 60 = 445 55x = 495 x = 9 sub into my definitions ...
October 25, 2016

Math
each side of the base ---- x ft height of box ------------ y ft x^2 y = 8 y = 8/x^2 cost = 6x^2 + 4xy = 6x^2 + 4x(8/x^2) cost = 6x^2 + 32/x
October 25, 2016

Algebra
second number ----- x first number ------- 2x - 183 solve for x: x + 2x-183 = 1161
October 25, 2016

Math
let the longer piece be x cm then the shorter piece is 14-x cm 14-x = (2/5)x times 5 70 - 5x = 2x 70 = 7x x = 10 the long piece is 10 cm, the shorter is 4 cm check: is 4/10 = 2/5 ? , YES
October 25, 2016

math
Most direct way: The volume of the rock equals the change in the volume of the tank. The change in the height was 4 cm. So the volume of the rock is (9)(15)(4) cm^3 = 540 cm^3 or, along your thinking volume of tank at the start = (9)(15)(8) or 1080 cm^3 volume after rock is ...
October 25, 2016

math
I have no idea what your x and y stand for, but in a rhombus, opposite angles are equal and adjacent angles add up to 180° So the other angle is 130°
October 25, 2016

Math
assuming 30 days in a month ... cost of one can per day from machine = 30(.75) = $22.50 cost using 12-pack = (4.99/12)(30) = 12.48 continue
October 25, 2016

Algebra 1
1. A - wrong 2. C - wrong 3. B - wrong 4. A - wrong How did you get your answers? Where you just guessing?
October 25, 2016

Algebra 1
I don't see any choices or any work Surely you don't expect somebody to just go ahead and do this assignment for you , do you? e.g. what steps would you take to answer the first one?
October 25, 2016

Mathematics
Just use your definitions: "first term of an Arithmetic Progression is -4" --> a=-4 "the 15th term is double the 5th" ---> a+14d = 2(a+4d) a + 14d = 2a + 8d 6d = a 6d = -4 d = -2/3 term 12 = a + 11d = -4 + 11(-2/3) = -25/3 check: is the 15th term ...
October 25, 2016

Algebra Two
2500 + .06s ≥ 3100 , where s is his sales .06s ≥ 600 s ≥ 600/.06 s ≥ 10,000
October 25, 2016

Maths GRE
correct
October 25, 2016

Maths GRE
correct , so D
October 25, 2016

Math
fathers age ---- 8x son's age ----- 3x but 8x = 48 x = 6 so the son is 18 or , just using a ratio .... 48/s = 8/3 8s = 144 s = 144/8 =18
October 25, 2016

math
If PQ = QR , (where P(6,-1), Q(1,3), R(x,8)) √( (3+1)^2 + (1-6)^2) = √( (8-3)^2 + (x-1)^2 ) √41 = √(x^2 - 2x + 26) square both sides 41 = x^2 - 2x + 26 x^2 - 2x - 15 = 0 (x-5)(x+3) = 0 x = 5 or x = -3
October 25, 2016

Math
average hourly change = (-21 - 63)/12 degrees/hr =
October 25, 2016

maths
http://www.jiskha.com/display.cgi?id=1477323150
October 24, 2016

maths
http://www.jiskha.com/display.cgi?id=1477323001
October 24, 2016

maths
I did this for you when you were Saphina AlMatary http://www.jiskha.com/display.cgi?id=1477322557 I gave you a good hint for the second one Did you even look at it?
October 24, 2016

Math
good call Steve! (at least I got the right answer, lol)
October 24, 2016

Math
The largest angle will be opposite the side 28 let it be 2Ø, so each bisected angle is Ø let the bisector form angles A and B along the 28 side, so that A + B = 180° --> B = 180-A and we know sinA = sin(180-A) = sinB let the 28 side be split into x and 28-...
October 24, 2016

maths
To talk about "roots" you need equations, you don't have any. anyway.... for 3x^2 - 6x - 7 = 0 , the sum of the roots is 6/2 or 3 and the product of the roots is -7/3
October 24, 2016

maths
check in your text or in your notes what properties are needed to investigate the nature of the roots. hint: it has to do with the determinant. btw. - I can't make your your last equation.
October 24, 2016

Math
clear case of the cosine law BC^2 = 4^2 + (3√3)^2 - 2(4)(3√3)cos30° carry on
October 24, 2016

maths
There is no unique or best way to solve these. After doing a few you get a "feel" of what to look for. e.g. for your first one, notice that last one says: y - 4z = 25 , so y = 25+4z - could be useful look at the first two, they both have 1x so lets subtract the 2nd ...
October 24, 2016

Math
What is your question? What does "and three points at the time of closing" mean?
October 24, 2016

maths
-did the first one for you - still waiting for your response to the second part of my reply http://www.jiskha.com/display.cgi?id=1477316621
October 24, 2016

Math Check Answers
both are correct
October 24, 2016

correction- math
Sara found the area. You want the perimeter = 2(12.75) + 2(8.25) = ..
October 24, 2016

maths
hard to tell which are your groups of equations.
October 24, 2016

Math Check Answers
answers: #1 - A #2 - D #3 - B
October 24, 2016

maths
x^2 - 6x = x^2 - 6x + 9 - 9 = (x-3)^2 - 9 3x^2 + 20x = 3(x^2 + (20/3)x + 100/9 - 100/9 = 3( (x + 10/3)^2 - 100/9 = 3(x+10/3)^2 - 100/3
October 24, 2016

maths
If the coefficient of x^2 is 1, look for 2 numbers which when multiplied give you the constant, and which when added give you the coefficient of the middle term that is, (-10)(4) = -40 (-10) + 4 = -6 so (x - 10)(x + 4) for the second one: 3x^2 + 20x - 7 = 0 , what method have ...
October 24, 2016

Math
make a sketch. split the figure into a rectangle and a right-angled triangle. in the triangle the base will be 21-13 or 8 cm and the hypotenuse is 17 let the height be h h^2 + 8^2 = 17^2 h^2 = 225 h = 15 area = rectangle + triangle = 13(15) cm^2 + (1/2)(8)(15) = 255 cm^2
October 24, 2016

math
to be divisible by 6, it must be divisible by 2 AND 3 8454 is even, so it is divisible by 2 the sum of the digits of 8454 is 21, which is divisible by 3, so 8454 is divisible by 3 (divisibility test for 3: if the sum of the digits of any number is divisible by 3, so is the ...
October 24, 2016

Math
What is C(4,3) ?
October 24, 2016

Math
π is indeed an irrational number , but Don Ho said π = 3.14, which is not true, since 3.14 = 314/100 or 157/50 and that would be a rational number all radicals that are not perfect squares, are also irrational number e.g. √5
October 24, 2016

MATH
You will need brackets in 6/(3-x) = (7-5x)/6 and (3-x)(7-5x) = 36 21 -22x + 5x^2 = 36 5x^2 - 22x - 15 = 0 (x - 5)(5x + 3) = 0 x = 5 or x = -3/5 the common ratio is 6/(3-x) if x =5, common ratio is 6/-2 or -3 if x = -3/5, common ratio is 6/(3 + 3/5) or 5/3
October 24, 2016

maths
I will assume this is an arithmetic sequence. Let's just use our formulas we know d = 2 sum(10) = 93 ---> n = 10, a = ? (10/2)(2a + 9(2)) = 93 5(2a + 18) = 93 10a + 90 = 93 10a = 3 a = .3 check: 10th term = a+9d = .3 + 18 = 18.3 sum(10) = (10/2)(first + last) = 5(.3+18....
October 23, 2016

maths percentage
You appear to have a typo ---- 3205% ????
October 23, 2016

maths need help too hard
4^x+3^x=9^x 4^x+3^x=3^(2x) 4^x = 3^(2x) - 3^x) 4^x = 3^x(3^x - 1 (4/3)^x = 3^x - 1 preliminary check: if x = 1 4+3 = 7 < 9 if x = 2 16 + 9 = 25 < 81 .. if x = 6 4^6 + 3^6 = 4825 < 9^6 for x ≥ 1, the gap between LS and RS is increasing, and RS > LS let's ...
October 23, 2016

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