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Posts by Reiny

Total # Posts: 38,374

precalculus
There are several question of your type in the Related Questions section below

precalculus
Vague question. are you converting an equation or a point with rectangular coordinates?

Maths
For any number, there are 10 possible digits for the unit place, one of those is the 2. so prob(your event) = 1/10

Algebra
compare: http://www.jiskha.com/display.cgi?id=1480210517

Algebra
find the vertex of the parabola. The t of the vertex tells you when it reached the maximum height, the h tells you what that height is.

Math
equation: y = 100 (2)^(t/3.2) .. .. to get 450 bacteria 450 = 100 (2)^(x/3.2) 4.5 = 2^(x/3.2) take log of both sides and use log rules (x/3.2)log 2 = log 4.5 x/3.2 = log 4.5/log2 x = 6.944 hrs. or appr 7 hours

precalculus
How does this post differ from this one? http://www.jiskha.com/display.cgi?id=1480198638

PreCalc
let f(x) = 2x^3+x^2-8x+3 f(1) ? 0 f(-1) = -2+1+8+3 ? 0 f(3) ? 0 f(-3) ? 0 f(3/2) = 0 , yeahhhh, 2x-3 is a factor by long division, 2x^3+x^2-8x+3 = (2x-3)(x^2 + 2x -1) the quadratic has roots of x = -1 ± ?2 looking at the graph of y = 2x^3+x^2-8x+3 -1-?2 < x < -1+?...

Algebra
let the distance from Seattle to wilderness be x miles x/420 + x/300 = 6 times 2100 the LCM 5x + 7x = 12600 x = 1050 miles

Trigonometry
look at the cos^-1 (x/3) construct a triangle with base of x and hypotenuse of 3 by Pythagoras: r^2 = x^2 + y^2 3^2 = x^2 + y^2 y^2 = 9 - x^2 y = ?(9-x^2) so we want the tangent tan (cos^-1 x/3) = opposite/adjacent = ?(9-x^2)/3

precalculus
(3(cos(5pi/4)+i sin (5pi/4) ) )^8 = 3^8(cos 8(5?/4) + i sin 8(5?/4)) = 6561( cos 10? + i sin 10?) = 6561( 1 + i(0) ) = 6561 B (3-3i)^6 let z = 3-3i, so we want z^6 r = ?(9 + 9) = ?18 = 3?2 plot (3,-3) which is in IV, so Ø = 315° or 7?/4 z = 3?2(cos 7?/4 + i sin 7?/4...

precalculus
I checked the first 4, they were ok you seem to know what you are doing.

Trigonometry
a) isn't arcsin(sin(?)) the inverse of itself? so 13?/16 b) and c) same thing, except by definition arcsin( ..) will give you the smallest positive angle so arccos(cos(-?/18) = ?/18 d) arcsec(-?2) the angle Ø so that secØ = -?2 or cosØ = (-1/?2) &...

precalculus
a) ok b) (i-j)-(18i+27i) = -17i - 28j c) (5i-5j)-(30i+54j) --> you did 5u - 5v instead of 5u-v

pre calculus
250 pounds at 45° ---> (250cos45, 250sin45) 130 pounds at -60° ---> (130cos(-60), 130sin(-60) ) Resultant = (250cos45, 250sin45)+(130cos(-60), 130sin(-60) ) = (125?2, 125?2) + (65 , -65?3) = ( 125?2 + 65 , 125?2 - 65?3) = appr (241.7767 , 64.1934) maginitude...

Discrete Math
if you meant: x^1 + x^2 + x^3 + 2x^4 + x^5 = 68 there are none http://www.wolframalpha.com/input/?i=solve+x+%2B+x%5E2+%2B+x%5E3+%2B+2x%5E4+%2B+x%5E5+%3D+68

pre calculus
checking for right-angled triangle: is 100^2 = 55^2 + 85^2 ? NO so let's find the smallest angle by the cosine law: 55^2 = 100^2 + 85^2 - 2(100)(85)cosØ cosØ = 14200/17000 = .83529.. Ø = 33.35..° , (I stored it for accuracy on my calculator So area...

pre calculus
u=<0,-4>, v=<-2,-8> a) 2v+u = <-4,-16) + <0,-4) = <-4, -20> b) 5u - v = <0,-20> - <-2,-8) = <2, -12> c) do this one the same way

Mathmatics help please
clearly 25 and 15

Maths help asap please
3c-7 > 5c+4 3c - 5c > 4+7 -2c > 11 c < -11/2 or c < -5.5 so the smallest integer that is a solution is c = -6 check: if c = -6, -18 - 7 > -30+4 -25 > -36 , true! if c = -5 -15-7> -25+4 -22 > -21 , false

Math
subtract 2 from each part, and you are done -3<x+2<3 -3-2 < x+2-2 < 3-2 -5 < x < 1 ---> ( x lies between -5 and 1 )

Math
nothing wrong with that you could just use the trig-vector notation resultant = (10cos60,10sin60) + (20cos120,20sin120) + (30cos180,30sin180) + (40cos270,sin270) = (5, 5?3) + (-10, 10?3) + (-30, 0) + (0, -40) = ( -35, 5?3-40 )) your sketch will confirm that

Trigonometry
Both Steve and I both told you what was wrong with the wording of the question. http://www.jiskha.com/display.cgi?id=1480115359 Did you even look at the responses?

Math
(2 x 3)>2 - 5>2 is a false statement. you are basically saying: 6 > 2-5 > 2 6 > -3 > 2 the part 6 > -3 is true, but -3 > 2 is nonsense To ask "evaluate" the expression makes no sense Hey, wait a minute! Did you mean (2 x 3)^2 - 5^2 ?? then you...

math
You can't just drop the variable. 5(2x + 7) = 10x + 35 Now you can see that we can't add the 10 and 35 since they are "unlike" terms

Math
correct

math
The 14M, the 3M and the 1M are all expenses so what is 20 - (14+3+1) ?? I get 2 Million

Calculus AB
3y^3 + 2x^2 = 5 9y^2 dy/dx + 4x = 0 dy/dx = -4x/9y^2 when y = 1 , 3 + 2x^2 = 5 2x^2 = 2 x = ± 1 , but in quadrant 1, x = 1 dy/dx = -4(1)/9 = -4/9 equation of tangent: y-1 = (-4/9)(x-1) 9y-9 = -4x + 4 4x + 9y = 13 check: http://www.wolframalpha.com/input/?i=plot+3y%5E3+%...

Trigonometry
y = cos(3?/4 - x) already is a single function of x, namely the cosine function. I don't understand what else you want to do with it. We know: using cos(A-B) = cosAcosB + sinAsinB cos(3?/4 - x) = cos 3?/4 cosx + sin 3?/4 sin x = -?2/2 cosx + ?2/2sinx = ?2/2 (sinx - cosx...

Math
In the original number let the unit place by x then the tens place is 2x, (obviously x < 5) then the number in terms of its value is 10(2x) + x and the number reversed is 10x + 2x the difference between these two is 36, just translate this into Math. 10(2x) + x - (10x + 2x...

Math
clearly the 5 has to go in the unit position for the number to be odd At the front, what would be bigger, something 6 hundred or something 8 hundred?

Mathematics
let his sales be x .06x + 6000 = 10200 solve for x

Maths
330/x - 330/(x+5) = 1/2 That's ok, we end up with a quadratic. Multiply each term by 2x(x+5) 660(x+5) - 660x = x(x+5) 660x + 3300 - 660x = x^2 + 5x x^2 + 5x - 3300 = 0 (x-55)(x+60) = 0 x = 55 or x = -60, we would reject the -60 So your inward speed is 55 km/h, the return ...

math
90 = 2x3x3x5 since each pair of equal factors produces a perfect square, we have 3x3, a perfect square. So all we need is another 2 and another 5 How about 2x2x3x3x5x5 = 900 900 = 30^2 , so it is a perfect square, and it is divisible by 90

math-factors and multiples
both 40 and 32 divide by 8 both a^3 and a^2 divide by a^2 The GCF is 8a^2

math
It is 30a^2

math
5 ? m/-3 + 18 add m/3 to both sides 5 + m/3 ? 18 m/3 ? 13 m ? 39 or 5 ? m/-3 + 18 -13 ? m/-3 times -3 39 ? m m ? 39 , same as above

math
the slope of the 2nd is -2/16 = -1/8 which is the negative reciprocal of the slope of the first. Thus, the lines are perpendicular.

math
I assume we are factoring 25m^6-121m^4 = (5m^3 - 11m^2)(5m^3 + 11m^2)

Calculus applications
let the height be 100 cm^3 ?r^2 h = 100 h = 100/(?r^2) S = 2 circles + the sleeve = 2?r^2 + 2?rh = 2?r^2 + 2?r(100/(?r^2)) = 2?r^2 + 200/r you typed it wrong, it should have been 2?r^2 + 200 r^-1 dS/dr = 4?r - 200/r^2 = 0 for a min of S 4?r = 200/r^2 r^3 = 200/(4?) = 25/? r...

Math
Now: Marcus ---- x John ------ x+10 5 years from now: John's age = x+15 5 years ago: Marcus = x-5 3(x+15) = x-5 that would give you the silly answer of x = -25 checking now Marcus is -25 John is -15 5 years from now, John is -10 and 5 years ago Marcus was -30 sure enough 3...

maths
Without any restrictions, number of committees = C(10,4) = 210 include at least one woman ---> exclude cases of all 4 being men number of ways = 210 - C(5,4) = 205

math
now: daughter ---- x years Mary -------- 3x years 4 years ago: daughter : x-4 Mary : 3x-4 (x-4)(3x-4) = 40 3x^2 -16x + 16 = 40 3x^2 - 16x - 24 = 0 I was expecting it to factor, hoping for whole number solution, but .... x = (16 ± ?544)/6 = 6.55 or a negative check: if ...

Math
let the two numbers be 9x and 3x then 9x + 3x = 72 .. x = 6 sub into my definition to get the numbers.

Math
Find the midpoint of AB, then use your "distance between two points" formula to get CM .

Maths
let the numbers be x and x+1 solve: x + x+1 = 39

math
your first equation should have been 4x +5 = 37 instead of 4x(5) = 37 but then you miraculously switched it to the right one as you solved it. The answer is correct

Further mathematics
x^2 + y^2 = 5xy complet the square: x^2 + 2xy + y^2 = 7xy (x+y)^2 = 7xy take log of both sides 2log(x+y) = log 7 + logx + logy 2log(x+y) - log7 = logx + logy 2log(x+y) - 2log 7^(1/2) = logx + logy 2[ log(x+y) - log ?7] = logx + logy 2 log( (x+y)/?7 ) = logx + logx as required ...

algebra~help me
18^(4-4y)=54(?2)^(3y-2) take log of both sides (4-4y)log18 = lof54 + (1/2)(3y-2)log2 4log18 - 4ylog18 = log54 + (3y/2)log2 - log2 4log18 - log54 + log2 = y( (3/2)log2 + 4log18) 3.58972... = (5.4726...) y y = .655941

Calculus
so considering t = 0 to correspond with 2016 1000 = A 3^0 , but 3^0 = 1 A = 1000 b) y(5) = 1000 3^(4/3) = .... Use your calculator c) 100000 = 1000 3^(t/4) 1000 = 3^(t/4 take log of both sides log 1000 = log 3^(t/4) 3 = (t/4)log 3 t/4 = 3/log3 t = 12/log3 = appr 25.15 years iv...

math
Assuming the farm is a rectangle ... length --- x width = 39 2x + 2(39) = 187.2 find x once you have x, take x/39

algebra
How about you showing me some of your steps, now that I have done two very similar to this one for you ?

algebra
breath (width) ---- x length -----------x+12 2x + 2(x+12) = 144 carry on

algebra
smaller --- x larger --- y Now just translate into Math. 3(y - x) = y+3 3y - 3x = y+3 3x - 2y = -3 ** 3(y+x) = 8x + 2 3y + 3x = 8x + 2 5x - 3y = 2 *** solve ** and *** You should get two whole numbers.

Differential calculus
If expanded you would get a standard cubic Its x-intercept are (2,0), (-1,0) and (-3,0) http://www.wolframalpha.com/input/?i=plot+y%3D(x-2)(x%2B1)(x%2B3)

maths
let the two numbers be 5x and 7x "it's lam is 210" , I have no clue what that means.

maths
I will assume you meant the ninetieth term. If a and d are the first term and common difference respectively, then term(90) = 30 a + 89d = 30 a = 30-89d sum(17) = (17/2)(2a + 16d) = (17/2)(2(30-89d) + 16d) = (17/2)(60 - 162d)

Math
Did you make a sketch? 1) sin30° = h/15 h = 15sin30 = 15(1/2) = 7.5 m Very unsafe way to place a ladder, the angle should be > 76° at the ground 2) in reference to the 60° angle, the 13 m is the "adjacent" and you want the "opposite" side ...

Statistics
numer of ways = 15 x 14 x 12 = .... (assuming the order matters, and you have specified positions)

Math
correct (the jet stream does not just flow over the US )

I dont know
they can be any (x,y) such that x^2 + y^2 = 64 e.g. (2 , ?60), (?39 , 5) , (8,0), (8,0), (4?2 , 4?2) etc

Algebra2
but log8 2 = 1/3 so log8 (a/2) = log8 a - 1/3

math
equilateral ---> all sides are equal, so 3x+2 = 2y-x 4x + 2 = 2y 2x + 1 = y also 3x+2 = y + 3 3x+2 = 2x+1 + 3 x = 2 then y = 5 so each side is 3x+2 = 8 and the perimeter is 24

Math
9/(2x) = 15/12 "cross-multiply" 30x = 108 x = 108/30 = 18/5 or 3.6

Math
amount of peaches --- x lbs amount of melons ---- y lbs amount of apples ----- 100 - x - y lbs (assume both x and y are whole numbers) 10x + 3.5y + .5(100-x-y) = 100 double every term 20x + 7y + 100 - x - y = 200 19x + 6y = 100 x = (100 - 6y)/19 , clearly 0 < y < 6 by ...

10th Grade Math
To have a triangle, the sum of any two sides must be greater than the third side. look at C 5+10< 18 all the others form a triangle

maths
The volume of 2 similar objects is proportional to the cube of its linear sides 320/x = 8^3/6^3 512x = 69120 x = 69120/512 = 135 or the side ratio is 6/8 = 3/4 old volume = 8(l)(w) = 320 lw = 40 new volume = 6(3l/4)(3w/4) = 54/16 lw = (54/16)(40) = 135

maths
surface area of smaller = 4? r^2 surface area of larger = 4?(3r)^2 = 36?r^2 which is 9 times as great or the area of similar objects is proportional to the square of their linear dimension, so 1^2 : 3^2 = 1 : 9

Algerbra
so it will differ only in the constant let the equation be y = -4x + b but (-8,-4) lies on it, so -8 = -4(-8) + b solve for b and write the equation.

Trigonometry
tanØ = 4/1 = 4 Ø = 75.96 The angle should be 76° by ratio: 4/1 = 16/x x = 4

Math
number of adult tickets sold = 3x number of children tickets sold = 5x 5x = 3x + 180 take over.

math
LCD is 5b a/5 +4/b = ab/5b + 20/5b = (ab + 20)/(5b)

Algebra
slope of main street = (33-17)/(-22+2) = -4/5 so slope of Grimes Blvd = +5/4 y - 9 = (5/4)(x-80) y = (5/4)x - 100+ 9 y = (5/4)x - 91

Math
Follow the same steps I just showed you in your previous problem.

Math
number of girls ---- 7x number of boys ---- 5x "there are 8 more girls 10 boys" makes no sense are you saying, "there are 8 more girls than boys" ? which translated into math would be 7x = 5x+8 take it from here

maths
done, see below

algebra
number of nickels ---- x number of dimes ----- x+10 number of quarters = 37-(x + x+10) = 27 - 2x value of coins = 5x + 10(x+10) + 25(27-2x) = 5x + 10x + 100 + 675 - 50x = 775 - 35 x

Math
I don't know, you did not state the rate of interest.

maths
volume of wooden rod = ?(2^2)(6) = 24? volume which is submerged = 12? So the volume in the cylinder will change by that amount ?(4^2)h = 12? 16h = 12 h = 12/16 cm = 3/4 cm new depth = 4+3/4 cm = 19/4 cm or 4.75 cm

maths
" ... is placed in the tin or floats exactly half 2.what is the New depth of water " Retype in proper English so I can understand it.

maths
OK, even though have always been told that we can't add apples and oranges, ..... let the amount of apples be x lbs amount of oranges ----- (52 - x) lbs 5.25x + 3.8(52-x) = 4.25(52) 5.25x + 197.6 - 3.8x = 221 1.45x = 23.4 x = 16.1 lbs of apples and 35.9 lbs of oranges appr...

math
cost = 7.2(12) = 86.4 18 eggs = 1.5 dozen so you sold 10.5 dozen at 7.5 return = 10.5(7.5) = 78.75 loss = 86.4 - 78.75 = 7.65

Maths
Four times as much, or 32 kg Can you show me why that is so?

maths
volume of ball = (4/3)?(4.5)^3 So that is the change in volume in the cylinder once removed ?(6^2) h = (4/3)?(9/2)^3 36h = (4/3)(729/8) = 243/2 h = 243/72 = 27/8 the water will fall 27/8 cm or 3.375 cm check my arithmetic.

Algebra 1
The boat will be .15 miles from Ellen coming and going away. So 1 - 70t = .15 OR -1 + 70t = .15 t = .01214... hrs or t = .01642.. hrs t = .01214(3600) sec or t = .01642(3600) sec t = 43.7 sec OR t = 59.1 sec

check - Math
ok, the cat's were adopted, that means the count was reduced by 120, not increased. I read the question incorrectly number of cats after adoption = 2x - 120 make the simple change in the equation and solve

Math
number of cats ---- 2x number of dogs ----3x after adoption: number of cats = 2x + 120 (2x+120) : 3x = 3 : 7 (2x+120)/(3x) = 3/7 14x + 840 = 9x 5x = -840 x is a negative, which is not possible. notice 2:3 = .66.. and 3:7 = .42 , which is < 2/3 How can the ratio of cats : ...

maths
Area of a triangle = (1/2)(ab)sinØ where a and b are sides with Ø as the angle between them. Your data is perfectly suited for that formula

found my error - Go with Steve - maths need help
The second equation had addition, I read it as another subtraction.

maths need help
Log (a+3) (base 9) - log b(base 9)= c + (1/2) log9 (a+3) - log9 b = c+1/2 log9 ((a+3)/b) = c+1/2 ---> 9^(c+1/2) = (a+3)/b 3^(2c+1) = (a+3)/b ** log (a-3) (base 3) + log b (base 3)=c - 1 log3 (a-3)+ log3 b = c-1 log3 ( (a-3)/b )= c-1 --> 3^(c-1) = (a-3)/b *** divide ** by...

Math
let the roots of ax^2+bx+c=0 be m and n then m:n = r:1 m/n =r/1 m = rn sum of roots = m+n = rn + n = n(r+1) = -b/a ** product of roots = mn = n^2 r = c/a *** divide ** by *** (r+1)/nr = (-b/a) / (c/a) = -b/c rc + c = -bnr rc + bnr = -c r(c + bn) = -c r = -c/(c+bn) For acr^2+(...

math
A standard rotation is 2?. So whatever angle you have either adding or subracting multiples of 2? will yield a coterminal angle. e.g 8?/3 -----> think 480° 8?/2 - 2? = 2?/3 -----> think 120° 8?/3 + 2? = 14?/3 -----> think 840° 8?/3 - 4? = -4?/3 -----> ...

calculus
c(x)=3x^3 - 12x^2 +9000x c ' (x) = 9x^2 - 24x + 9000 = 0 for a max/min of c(x) 9x^2 - 24x + 9000 = 0 This equation has no real solution. c(0) = 0, for all values of x > 0, c(x) increases so our minimum cost is when we don't produce anything, (that actually makes ...

Math
If you are referring to your previous post, look at my reply to it.

Math
For any number to be divisible by 6, it must be divisible by both 2 and 3 To be divisible by 2, the unit digit must be even or zero, so that eliminates A - 5. To be divisible by 3, the sum of the digits must be a multiple of 3 (divisible by 3) Since we have a sum of 8 for the ...

Algegra
So let's just change Ax + By = C to the form y = mx + b Ax + By = C By = -Ax + C divide each term by B y = (-A/B)x + C/B So compare that to y = mx + b m = -A/B so I have just developed a quick way to find the slope of any equation in general form e.g. 7x + 9y = 17 has slpe...

Math
so with her new test, there will be 6 tests (sum of what you have so far + x)/6 = 69 solve for x

maths
original fraction --- x/y first new fraction: (x+1)/(y+1) = 2/3 3x + 3 = 2y + 2 3x - 2y = -1 ** second new fraction: (x-2)/(y-2) = 3/5 5x - 10 = 3y - 6 5x - 3y = 4 *** solve the two equations ** and ***

mathematical methods for economics
Did you try Venn diagrams? Start filling in from the intersection of all three circles. Put 50 in that intersection, then work your way outwards from there.

Math, Surds
let the length of each side be s s^2 = 60 s = ?60 = ?4*?15 = 2?15 each side is 2?15 m perimeter = 8?15 m

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