Wednesday

April 23, 2014

April 23, 2014

Total # Posts: 26,103

**cal**

f(x) = x^-2 - 2x - 8 f ' (x) = -2x^-3 - 2 f '' (x) = 6x^-4 extrema: -2/x^3 = 2 x^3 = -1 x = -1, f(-1) = 1 - 2(-1) - 8 = -5 at x = -1, f ''(-1) is > 0, so (-1,-5) is a minimum my answer confirmed by http://www.wolframalpha.com/input/?i=plot++y+%3D+1%2Fx%5...

**check: Algebra 1**

I assumed your constant would have been correct, wrong assumption. go with kuai's solution, but write it as x- 2y = -7

**Algebra 1**

It is considered "poor form" to have the equation in standard form start with a negative x or containing fractions. so the 1st one I would write as x - y = -8 the last one: firs of all it should have been (-1/2)x + y = 23/2 multiply each term by -2 x - 2y = -23

**geometry**

correct

**geometry**

dodecagon --- 12 sides It must be regualar, that is, all sides must be equal and all 12 interior angles are equal. sum = 180(n-2) so each angle = 180(n-2)/n for 12 sides: each angle = 180(12-2)/12 = 150° you do the one with 20sides

**6th grade math**

nope http://www.wolframalpha.com/input/?i=plot+%281%2C5%29%2C+%282%2C5%29%2C+%283%2C5%29%2C+%284%2C5%29 notice all their y values are the same, y = 5 so it is a horizontal line

**math**

Your question makes no sense to me What is $150 ? Is the 8% rate compounded monthly? What is the $12.87 supposed to represent? You did not define m, r and t

**algebra**

Is what answer true or false ?? 8x-2 = -9+7x x = -7

**LOL @ Steve --**

Hilarious Captain: What happen ? Mechanic: Somebody set up us the bomb. Operator: We get signal. Captain: What ! Operator: Main screen turn on. Captain: It’s you !! CATS: How are you gentlemen !! CATS: All your base are belong to us.

**MATH**

Great read: Outliers by Malcolm Gladwell

**College Algebra**

your equation only has one variable. 5x + 3y = 60 3y = -5x + 60 y = (-5/3)x + 20 the y intercept of 20 ( or y = 20) gives you the number of gumballs (y) you can buy for 60 cents if you buy zero mints.

**cal**

f'(x) = 6x^2 - 6x - 12 = 0 for a max/min (critical value) divide by 6 x^2 - x - 2 = 0 (x-2)(x+1) = 0 x = 2 or x = -1 so, yes, x=2 is a critical number, (the other is x = -1) f '' (x) = 12x-6 f(2) = 2(2^3) - 3(2^2) - 12(2) + 18 = -2 f '' (2) = 24-6 > 0 si...

**clarification - math(help)**

Just because one of the numbers is a prime, does not mean the fraction is in lowest terms. e.g. 13/26 = 1/2 21/7 = 3 the numerator and denominator have to be "relatively prime", that is, no whole number exists that divides into both of them

**math(help)**

Why didn't they just ask, " Is 138435 evenly divisible by 3 ? " yes it is. is 38/53 in lowest terms? yes it is, since no whole number divides into both 38 and 53 here is a little-known trick: find a key a b/c on your calculator enter: 38 a b/c 53 = you will g...

**Maths**

I will assume that the building with side BC is on top of the cliff and A is at the bottom of the cliff. step1: tan44= AB/200 AB = 200tan44 so AC = 80 + 200tan44 let angle CPA = Ø tanØ = AC/200 = (80 + 200tan44)/200 tanØ = 1.365 Ø = 53.79°

**cal**

I will assume that you meant f(x) = 2x^(3/2) - 6x^(1/2) (or else we could just divide out the 2's in the first term) f ' (x) = 3x^(1/2) - 3x^(-1/2) f '' (x) = (3/2)x^(-1/2) + (3/2)x^(-3/2) or (3/2)( 1/√x + 1/(x√x) )

**6th grade math**

1. all three are correct 2. "they ate 1/5 of the bag" is not clear Did they eat 1/5 of a full bag, or Did they eat 1/5 of what was in the bag when she arrived?

**Algebra 1**

y+4 = x-2 y = x - 6 ---> usually called the y intercept - slope form or x - y = 6 ---> some texts call this standard form and this x-y - 6 = 0 ---> general form

**Algebra, URGENT!!!**

1. x^2 + (x+6)^2 = 8^2 x^2 + x^2 + 12x + 36 - 64 = 0 2x^2 + 12x - 28=0 x^2 + 6x - 14 = 0 x^2 + 6x = 14 , completing the square .... x^2 + 6x + 9 = 14+9 (x+3)^2 = 23 x+3 = ± √23 x = -3 ± √23 but x has to be positive so x = √23 - 3 so one leg is &...

**College Algebra**

A = 25000 e^(.06(5)) A = 25000 e^.3

**home school**

let the numbers be x and y x+y = 42 ---> y = 42-x xy = 185 --->x(42-x) = 185 42x - x^2 - 185 = 0 x^2 - 42x + 185 = 0 (x-37)(x - 5) 0 x = 37 or x = 5 then y = 42-37 or y = 42-5 y = 5 or y = 37 (symmetric solution) the two numbers are 5 and 37

**Algebra NEED HELP ASAP!!!!!!**

T = 4h + 72 , 0 < h < 12, where h is the number of hours at noon , h = 6 T = 72 + 4(6) = 96

**cal**

did you mean it the way you typed it, or did you mean f(x) = √(x+2) ? I will assume f(x) = √(x + 2) judging by the values of the interval first take the definite integral of the function = ∫(x+2)^(1/2) dx from 1 to 7 = (2/3)(x+2)^(3/2) | from 1 to 7 = (2/3)9^...

**Math Properites**

= (3.4)(3.8)(10^5)(10^-9) = 12.92(10^-4) = 12.92/10000 = .001292

**TRIANGLE SIMILARITIES RATIOS AND PROPORTIONS**

The key to this question is to realize that all the right -angled triangles are similar, and have the ratio of 3:4:5 in the length of their sides. Mark the two angles in triangle BCD with o and x ( you should be able to see that since XD | BC , so you can mark XDC as o and DCX...

**Pre-Calculus**

did you notice that f(x) = (x-9)(x-2)/(x-9) ?? = x-2, x ≠ 9 So for all values of x except x=9 the given function reduces to f(x) = x-2 which is a straight line. when x = 9, the original gives you 0/0 which is indeterminate, while the reduced function gives you (9,7) So t...

**algebra 2**

Prob(cheese, then turkey) = (6/15)(5/14)= = 30/210 = 1/7

**MATHS**

all multiples of 7 are $1 7, 14, 21 ------- $3.00 all multiples of 6 are .50 6,12,18,24,------- 4(.50) = $2.00 all multiples of 5 are .20 5,10,15,20 ---- 4(.20) = $.80 all multiples of 4 are .10 4,8,12,16,20,24 but the 12, 20 and 24 have been changed, so only the 4,8, and 16 c...

**Advanced Funtions**

if either x or y , or both = 0

**Advanced Functions**

They were the most obvious ones.

**Advanced Functions**

sin 60° = √3/2 cos 30° = √3/2 sin 120° = √3/2

**PRECALCULUS**

solve both as quadratics that factor 1. 2cos^2 x - 5cosx + 2 = 0 (2cosx - 1)(cosx - 2) = 0 cosx = 1/2 or cosx = 2 but cosx = 2 is not possible, since -1 ≤ cosx ≤ +1 for cosx = 1/2, since it is positive, x could be in I or IV x = 60° or x = 360-60 = 300° 2. ...

**Advanced Functions**

if cosx = 5/13, (recognize the 5,12,13 triangle ?) sinx = 12/13 tanx = 12/5 if cosy = -5/13 and y is in III siny = -12/13 tany = 12/5 2sinx+2siny+2cosx-2tanx+tany+2cosy = 2(12/13) + 2(-12/13) + 2(5/13) -2(12/5) + (12/5) + 2(-5/13) = - 12/5 or -2.4

**Trig - Law of sines and cosines**

I started with AB, the vertical diagonal of the square. I then drew square ALMN At M, I drew the base BC of the equilateral triangle perpendicular to AM, letting BM = MC = 2 Joi AB and AC for the triangle. Let the intersection of ML and AB be P, and the intersection of MN and ...

**algebra 2**

What is your question? What does "3/4 Six lots" mean?

**algebra**

BTW, Steve answered you yesterday when you posted it then. Did you not look at his answer?

**algebra**

prob(rain on Sat and Sun) = (10/100(30/100) = (1/10)(3/10) = 3/100 or 3%

**Algebra**

multiply each term by ab, the LCD bx - ab = ay y = (bx - ab)/a or just multiply both sides by b bx/a - b = y , which is the same as my first result

**algebra**

let the amount invested at 11% be x so .11x + .12(x+4000) = 940 .11x + .12x + 480 = 940 .23x = 460 x = 2000 So originally you had $2000 in the 11% account and $6000 in the 12% account at the end you had 2220 and 6720 respectively check: 2220+6720-8000 = 940

**Geometry (math)**

True No need to draw a figure, just look at the screen on your computer. let s be the top of the screen let q be perpendicular of your screen, how about the left side? let p be the bottom of your screen Is the top of your computer screen not parallel to its bottom?

**Math**

geesh, forgot to put D) in front D) which means that for every increase of 1800 feet, the temperature would decrease by 1° or for every decrease of 1800 ft , the temperature would rise by 1° F B) so how did Tessa get +.9/-.5 ? look at the bottom number of -.5. where di...

**Math**

clearly Gemma used the first two pairs, just check the calculations. B) which difference in the first elements would give you -.5 ?? c) no matter which pair you take you get a slope of -1.8 or -1.8 : 1 or -1800 ft : 1° F which means that for every increase of 1800 feet, th...

**math**

prob(yellow) = x/(20+x) but we know this is 1/6 x/(20+x) = 1/6 6x = 20+x x = 4 so there are 24 balls, of which 9 are blue so Prob(blue) = 9/24 = 3/8

**Math questions**

think of 8 as the slope and (12,240) as an ordered pair for this relation y = -8x + c at (12,240) 240 = -8(12) + c c = 336 y = -8x + 336 so when x = 0, y = 336 Where was he when x = 0 ???? at ground, y = 0 solve 0 = -8x+240 8x = 240 etc ....

**algebra**

What do you think? I don't see your choice of answer for any of them.

**Pre-Calculus**

since the line is perpendicular, their slopes are negative reciprocals of each other, that means, they must be OPPOSITE in sign so first slope = -3/2 2nd slope = +2/3 y-2 = (2/3)(x-4) 3y-6 = 2x-8 3y = 2x - 2 y = (2/3)x - 2/3

**Math Help**

#2 is correct #3 solving your 2 equations: 1st times 2: 8b+6n=47 2nd times 3: 15b+6n=64.5 subtract them: 7b = 17.5 b = 2.5 sub back in ----> n = 4.5 necklace costs $4.50 and bracelet costs $2.50 so buying just one each = $7.00

**Math Help**

first one: your equation: B = 22 +11.5w , where B is the balance, and w is the number of weeks or y = 22+11.5x to make it fit your x = 8 your friend: y = 218-13x if x = 8, you will have 22+11.5(8) = 114 your friend has 218-13(8) = 114 What do you think? Give the other two a sh...

**Math**

number of small posters x number of large posters y cost of small posters 240/48 = 5 cost of larger posters 240/30 = 8 5x+8y=240 to graph it, I would use intercepts let x = 0, y = 30 --->(0,30) let y = 0 , x = 48 ---> (48,0) slope = (0-30)/(48-0) = -5/8 For each reductio...

**Geometry**

Use the results of the ratio properties I gave you in your previous post

**geometry**

For the question to be "workable", AF is probably the median, with F on BC remember the centroid cuts the median in the ratio of 2:1, or AG:GF = 2:1 then FG:AF = 1:3 (x+8)/(9x-6) = 1/3 9x - 6 = 3x + 24 6x = 30 x = 5

**My fuzzy thinking - math**

Forget my previous post, r could be 1.5 my program line 60 should say: 60 if (b*c*d)^2 = (a*b*c^2*d*e) then print a;b;c;d;e and I got 64 96 144 216 324 80 120 180 270 405 96 144 216 324 486

**math**

I think I missed the obvious Since a,b,c,d,e are integers in GS, the smallest value of r is 2 a - b - c - d - e 51 102 204 408 816 52 104 ... 53 .... infinite number of choices for a so... still a silly question

**For Steve - math**

Crazy question. Agree with you, there has to be more As it stands: b/a = c/b and c/b = d/c and d/c = e/d b^2 = ac , c^2 = bd , d^2 = ed then b^2 c^2 d^2 = abcde I then ran this "primitive" BASIC program 10 for a = 50 to 100 20 for b = 51 to 100 30 for c = 52 to 100 4...

**Calculus**

Write it as f(x) = 7x^-2 - 6x^-6 F(x)= -7x^-1 + (6/5)x^-5 + c F(2) = -7/2 + (6/5)/2^5 + c = ......

**Calculus**

let the side of the square be x let the side of the triangle be y 4x + 3y = 40 x = (40-3y)/4 height of triangle from the 30-60-90 triangle ratio = √3/2 y area of triangle = (1/2)(y)(√3/2 y) = (√3/4)y^2 area of square = [(40-3y)/4]^2 = (1600 - 240y + 9y^2)/16 ...

**TO ANY MATH HELPERS**

1. from the 1st equation: x = 3y+1 into the 2nd: 3(3y+1) - y +1 = 0 9y + 3 - y +1 = 0 8y = -4 y = -1/2 sub into 2nd: 3x - (-1/2) + 1 = 0 3x = -3/2 x = -1/2 Do #2 the same way from the 2nd: y = 2x+4 etc (Just stating the answers is not acceptable and serves no purpose)

**math and physics**

asks for login and password

**math**

just did it http://www.jiskha.com/display.cgi?id=1384818273

**math**

36 = 1x36 = 2x18 = 3x12 = 4x9 = 6x6 = 9x4 = ....

**Math**

1 more than half of x should be x/2 + 1

**math**

To add/subtract something, they must be in the same units e.g 5 apples + 8 oranges = 13 appleoranges? so 2 hrs, 45 minutes = 2 + 45/60 = 2.75 hrs 3hrs, 57 minutes = 3 + 57/60 = 3.95 hrs now you can add them: 2.75+3.95 = 6.7 hrs = 6 hrs + (7/10)(60) minutes = 6 hrs, 42 minutes ...

**math**

As an after-thought ..... Tn = T(n-1) + 4 , T1 = -40 , n > 1 In the recursive notation, the initial value has to be included or else you can't begin your sequence.

**Precalculus**

tanØ secØ = tanØ tanØ secØ - tanØ = 0 tanØ(secØ - 1) = 0 tanØ = 0 or secØ = 1 if tanØ = 0 Ø = 0, 180°, 360° ... , 180k° , where k is an integer if secØ - 1 then cosØ =...

**Precalculus**

sec(Ø + 81) = 2 cos(Ø + 81) = 1/2 I know cos 60° = 1/2 so Ø+81 = 60 or Ø+81 = 300° Ø = 60-81 = -21° or Ø = 219° now the period of cos(Ø+81) = 360° so adding 360 will give me another answer so Ø = -21 +...

**math**

lots of missing information What was the rate of interest? Did he make any monthly payments? Did he make not payments except the one at the end of 31 months?

**Math-Algebra**

A direct square variation is a quadratic Given any 3 points , I can find that quadratic, but we can't "force" a fourth point on it. e.g A = 20.115r^2 - 101.835r + 135.78 produces the first 3 points , but not the last one

**Math-Algebra**

What is the topic for this question? Are you learning about "curve fitting" ?

**Math-Algebra**

Not enough data to see a pattern http://www.wolframalpha.com/input/?i=plot+%282%2C12.57%29%2C+%283%2C11.31%29+%2C+%284%2C50.28%29%2C+%285%2C78.56%29

**math**

x(1.07)^1 = 6100 x =6100/1.07 = $5700.93

**stats**

Play around with this website, it is great http://davidmlane.com/hyperstat/z_table.html click on "value from an area" enter 1 - .011 or .989 in "area" click on "below" and recalculate

**Question About Math**

correct for #1, wrong for #2 #2 If x is cost of buritos, y is cost of tacos "3 burritos and 4 tacos costs $11.33" --->3x+4y = 11.33 "9 burritos and 5 tacos costs $23.56" ----> 9x + 5y = 23.56 B !!!! Now , how easy was that? Notice how I just translate...

**Question About Math**

#1 should be obvious since d is "dime", it has to be multiplied by 10 (10 cents in a dime) and n is "nickels" it has to be multiplied by 5 So what do you think? #2, Once you define what x and y represent, the answer should be obvious as well. I would have u...

**Math**

I assume you made a diagram showing the highway and the road at 90° and the cop at 225 ft from the highway. let the moving car's position be x ft from the intersection, and Ø be the angle. then x/225 = tanØ x = 225tanØ 1 = 225 sec^2Ø d&Oslas...

**Finance**

80% of2800000 = 2240000 2240000 = 22000( 1 - (1+i)^-360)/i 101.81818.. = ( 1 - (1+i)^-360)/i 101.818182i = 1 - (1+i)^-360 (1+i)^-360 = 1 - 101.818182 i Now that is tough equation to solve. In the "olden days" we used interpolation. Even Wolfram, at least in its simpl...

**Math**

now, end of 0 months :2 at the end of 1 month :4 at the end of 2 months = 8 or 2^3 ... at the end of 6 months = 2^5 = 32 rabbits, or 16 pairs

**Algebra 1 Problem**

1. -26 < 4k-2 -13 < 2k-1 so now you have -13 < 2k-1 and 2k-1 < 5 which can be written as -13 < 2k-1 < 5 solving: add 1 -12 < 2k < 6 divide by 2 -6 < k < 3 since both "ends" are < draw an open circle at -6 and 3, join them with a solid...

**Math:)**

For Brandon's car to have m = 12000 100w + 10000 = 12000 100w + 10000 - 10000 = 12000 - 10000 100w = 2000 100w/100 = 2000/100 w = 20 part 2: obviously there has to be a second equation, which you did not include. Anyway, just set the two equations equal to each other and s...

**math**

prob of landing on blue = 2/7

**math**

Just use Pythagoras ... x^2 = 30^2+30^2 = 1800 x = √1800 = 30√2 or the 30-3--x triangle is similar to the 1-1-√2 right-angled triangle so x = 30√2

**finance**

PV = 50000(1.04)^-30 = $15,415.93

**math**

This is just like find the LCM of 8 and 10 which would be 40 must buy 40/8 or 5 packages of buns ---> 40 buns and 40/10 or 4 packages of hotdogs ----> 40 hotdogs

**math**

time = 8 years , 155 days = 8 + 155/365 = 8.42466 x e^(8.4266(.0895)) = 225500 x = $106092.70

**Math**

varies directly with the cube of their scale factor e.g if the scale factor is 1: 12 ( 1 inch = 1 foot) and a tiny table weighs 20 g then the full size table would weigh 12^3(20 g) or 34560 g which would be 34.56 kg

**Math**

10259 ft = 3419.67 yds correct to 2 decimal places as required.

**staistics, is it right?**

see http://www.jiskha.com/display.cgi?id=1384488019

**Math**

greens ---- x reds ------ 4x x + 4x = 50 take over.

**algebra please help!!!!**

multiply both sides by -11/20 (-11/20)(-20/11)y < (-9/17)(-11/20) y < 99/340 notice I reversed the inequality sign, since I multiplied by a negative.

**Math**

see http://www.jiskha.com/display.cgi?id=1384486281

**statistics**

to get the mean, add them up , then divide by 7 I get 168/7 = 24 (how can the average of your numbers possibly be 335 ??? The average must always lie between the smallest and the largest) your median and mode are correct

**Algebra 1 (Reiny or Kuai)**

not sure what you mean by "any lines of the graph", are you talking about the x or y axes ? if a line is horizontal, then it must cross the y-axis and all horizontal lines are functions if a line is vertical, then it must cross the x-axis, it is NOT a function any ot...

**Algebra**

I assume you are learning about Markov's chains in the study of matrices end of year 1: [4200 4800] x .88 .12 .72 .28 = [7152 1848] end of year 2 [7152 1848] .88 .12 .72 .28 = [7624.32 1375.68] I am not absolutely sure if I have the correct order, haven't done this kin...

**pre-alg Answer Check**

If this is supposed to be the equation x/2 = 9/4 , then 4x = 18 x = 4.5

**statistics**

z-score = (88 - 75)/10 = ....

**math**

What is 7! ?

**math**

what is 5000(1 + .06/12)^60 ?

**math**

Lexi's amount --- x Maria's amount --- 250-x Lexi spent 2/5 of x, so she has 3x/5 left Maria spends 40, so she has 250-x-40 or 210-x left 3x/5 = 210-x times 5 to get rid of fractions 3x = 1050 - 5x 8x = 1050 x =131.25 So Lexi had $131.25 and Maria had 118.75 check: Lex...

**Pre calculus**

cos(Ø - 42°) = -1 I know cos 180° = -1 Ø - 42 = 180 Ø = 222° , only one solution between 0° and 360° (look at the graph of cos Ø ) The period of cos(Ø-42) is 360° so a general solution is Ø = 222° + 360k°...

**math**

I did this for you on Tuesday. http://www.jiskha.com/display.cgi?id=1384305313 What part of my solution did you not like ?

**interest math**

How are you getting your answers ??? a) interest = 5000(.09)(80/365) = 98.63 b) value = 5000 + 98.63 = $5098.63 c) look at a calendar, count 80 days starting April 13 as one, april 14 as 2 , etc

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