Friday

October 21, 2016
Total # Posts: 36,321

**Math**

2000(1+i)^2 = 24200 (1+i)^2 = 1.21 take √ of both sides, etc

*August 21, 2016*

**please help with this trigonometric identity!**

I am sure that you meant: (cos 'a' - cos 'b') / (sin 'a' + sin 'b') + (sin 'a' - sin 'b') / (cos 'a' + cos 'b') = 0 the LCD is (sina + sinb)(cosa + cosb) LS = ( (cosa - cosb)(cosa + cosb) + sina - sinb)(sina - ...

*August 19, 2016*

**Maths Algebra**

3(5x-7)-2(9x-11)=4(8x-13)-17 15x - 21 - 18x + 22 = 32x - 52 - 17 -35x = -70 x = 2 check: LS = 3(10-7) - 2(18-11) = 9 - 14 = -5 RS = 4(16-13) - 17 = 12 - 17 = -5 my answer is correct

*August 19, 2016*

**Maths Squares and Square roots**

The sum cannot be found without some kind of addition somewhere, but .... look at the last one: add the first and last ---> 22 add the 2nd and 2nd last ---> 22 add the 3rd and 3rd last ----> 22 how such pairs of 22 can you find? If you have an odd number of terms, do ...

*August 19, 2016*

**Maths Triangles**

Too messy to type here. That proof should be in most textbooks, if not, Google it. https://search.yahoo.com/search?fr=spigot-nt-gcmac&ei=utf-8&ilc=12&type=692858&p=proof%20:%20sum%20of%20angles%20in%20a%20triangle%20equals%20180

*August 19, 2016*

**Maths Quadrilaterals**

Once you have proven that the sum of the angles in a triangle is 180° ..... in your quad, draw in any diagonal to create two triangles. So ......

*August 19, 2016*

**Maths Time and Work**

Poorly worded. By "rates of working" , do you mean the amount of work done, or the time taken to do the same job.

*August 19, 2016*

**Maths Unitary Method**

The key word in the first part is "or" men's rate = 875/5 = .. women's rate = 875/7 = ... then 10(men's rate) + 7(women's rate) = ... (politically incorrect question)

*August 19, 2016*

**Maths Percentage**

what is 54000/1.1 ?

*August 19, 2016*

**Maths Compound Interest**

count = 512000(1.025)^2 = .....

*August 19, 2016*

**Maths Compound Interest**

When is 1000(1.10)^n = 1331 ? 1.1^n = 1.331 take log of both sides, and use log rules n log 1.1 = log 1.331 n = log 1.331/log 1.1 = .... you do the button pushing

*August 19, 2016*

**geometry**

Well, you know that that the area of a triangle = (1/2)bh, where b is the base and h is the height but you are told that h = 3b , so area = (1/2)(b)(3b) 27 = (1/2)(3b^2) times 2 54 = 3b^2 b^2 = 18 b = √18 or 3√2 ft base = 3√2 ft and the height is 9√2 ft...

*August 19, 2016*

**Correction - Maths**

I obviously got x = 360 So there are 360 marbles, I have no idea where I got the 510 from, and then I copied it again at the end. Time for my third cup of coffee.

*August 19, 2016*

**Maths**

let the total be x (2/5)x = r , also b+54 = (2/5)x b = 2x/5 - 54 = (2x - 270)/5 b : y = 5 : 7 5y = 7b y = (7/5)b y = 7(2x-270)/25 so 2x/5 + (2x-270)/5 + 7(2x-270)/25 = x times 25 10x + 10x - 1350 + 14x - 1890 = 25x -9x = -3240 x = 360 we have 510 marbles check: red = (2/5)(360...

*August 19, 2016*

**math**

I had done this for you. http://www.jiskha.com/display.cgi?id=1471418592

*August 17, 2016*

**Analytic Geometry**

Since you know the vertex, your equation must be x = a(y-0)^2 + 0 , if the axis of symmetry is horizontal x = ay^2 but (3,5) lies on it, so 3 = a(25) a = 3/25 x = (3/25)y^2 or 25x = 3y^2

*August 17, 2016*

**Maths**

cos(A+B) = cosAcosB - sinAsinB apply it to your question

*August 17, 2016*

**Math**

log3 9^4 = 4 log3 9 = 4(2) = 8 or , just think it through 9^4 = 3^8 so log3 3^8 must be 8

*August 17, 2016*

**math**

first number --- x 2nd number ---- 1/x x + 1/x = 3 x^2 + 1 = 3x x^2 - 3x + 1 = 0 using competing the square: x^2 - 3x + 9/4 = -1 + 9/4 (x + 3/2)^2 = 5/4 x + 3/2 = ± √5/2 x = -3/2 ± √5/2 x = (-3 + √5)/2 or x = (-3 - √5)/2

*August 17, 2016*

**Math**

assuming that "a" is the base - log a x^6 y^7 = -(loga x^6 + loga y^7) = -(6loga x + 7loga y) = -6loga x - 7loga y none of your choices are correct, unless there is a typo with that minus sign

*August 17, 2016*

**Math3c**

Just use the definitions of an AP and translate the English to Math. "the sum of the first three terms" = a + a+d + a+2d = 3a + 3d "the sum of the next four terms" = a+3d + a+4d + a+5d = 3a + 12d given: "the sum of the first three terms is one half the...

*August 17, 2016*

**Pre Cal**

Show me your expansion, and I will check it. Did you remember that i^2 = -1 ?

*August 17, 2016*

**Pre Cal**

take a look at this question I did several years ago http://www.jiskha.com/display.cgi?id=1315862859

*August 17, 2016*

**Calculus**

I will assume you mean: y = x^3 + 3x^2 , notice how we show exponents here x^3 + 3x^2 = 0 x^2(x + 3) = 0 finish it up

*August 17, 2016*

**math**

wherever you see y, replace it with 2 and evaluate

*August 17, 2016*

**Algebra**

1. let his actual speed by x km/hr time to do his 40 km trip = 40/x let his supposed speed be x+1 km/h time taken = 40/(x+1) 40/x - 40(x+1) = 2 times x(x+1) , the LCD 40(x+1) - 40x = 2x^2 + 2x 2x^2 + 2x - 40 = 0 x^2 + x - 20 = 0 (x+5)(x-4) = 0 x = 4 or a negative he went at 4 ...

*August 17, 2016*

**Math**

clearly, (f + g)(x) = 5x - 3 which is linear, thus the domain is the set of all real numbers.

*August 17, 2016*

**Math**

For P(a,b) and Q(c,d) the midpoint M is ( (a+c)/2 , (b+d)/2 ) apply this to your problem

*August 17, 2016*

**math**

cost price of cheaper chocolates = 1.50/10 = .15 each cost of expensive chocolates = .20 let the number of each type of chocolates be x cost price = .15x + .2x = .35x selling price = 4/20 = .2 each return on sale = 2x(.2) = .4x .4x - .35x = 10 .05x = 10 x = 200 he bought 200 ...

*August 17, 2016*

**math**

Hard to understand your notation. I will assume you mean: 4.5 kg at 600 per kg ----> 2700 2 kg at 1200 per kg -----> 2400 3 kg at 1500 per kg -----> 4500 total = 9600 leaving 10000-9600 = 400

*August 17, 2016*

**math**

did you mean "Roman numeral" ? 1959 ----> MCMLIX http://www.rapidtables.com/convert/number/roman-numerals-converter.htm

*August 17, 2016*

**physics question**

Look at this question answered by Damon over 5 years ago, just change the numbers to fit your question. http://www.jiskha.com/display.cgi?id=1296412513

*August 17, 2016*

**Pre-calc**

6csc Ø - 5 = 1 csc Ø = 6/6 = 1 then sin Ø = 1 consider the sine curve and it is clear that Ø = π/2 or ±2π + π/2 or ±4π + π/2 ... for the given interval, Ø = π/2 general solution: Ø = π/2...

*August 16, 2016*

**Math**

The first question can be answered in 2 ways for each of those, the 2nd question can be answered in 2 ways, so 2^2 or 4 so far ... number of ways = 2^5 = 32

*August 16, 2016*

**Calculus**

by simple inspection, and knowing the rules of derivatives for sine and cosine .... no need for substitution. ∫sin(x)cos^2(x)dx = (-1/3) cos^3 x + c

*August 16, 2016*

**math algebra**

I assume you meant: 10, 2, 2/5, 2/25 clearly a = 10 , r = 1/5 you should know your formulas. term(n) = ar^(n-1) term(7) = 10(1/5)^6 = 10/15625 = 2/3125

*August 16, 2016*

**algebra**

Just did this. Why are you changing names and repeating the question ?

*August 16, 2016*

**math**

let the unit digit be x and the tens digit by y then the original number is 10y + x and the number reversed is 10x + y 10x + y - (10y + x) = 18 9x - 9y = 18 x - y = 2 but we also know that xy = 24 it should be obvious that the two number are 6 and 4. Since reversing the ...

*August 16, 2016*

**Math**

According to the wording of the question, your answer is correct Now -- 5 at end of month 1 = 5(2) = 10 at end of month 2 = 5(2^2) = 5(4) = 20 at end of month 3 = 5(2^3) = 5(8) = 40 ... at end of month 8 = 5(2^8) = 5(256) = 1280

*August 16, 2016*

**Math**

recall that area of triangle = (1/2) base x height 36 = (1/2)(base)(9) multiply both sides by 2 72 = 9base base = 72/9 = 8

*August 16, 2016*

**Algebra**

how about this way: using (ab)^n = (a^n)(b^n) (4x^-1)^-1 = (4^-1)(x^-1)^-1 = (1/4)(x^1) = (1/4)x or = x/4 #2 (x^3+3x^2+3x+1)^(-2/3) = 1/(x^3+3x^2+3x+1)^(2/3) notice I assumed your exponent was -2/3, the way you typed it, the exponent would have been -2 , with 3 a divisor ( (x^...

*August 16, 2016*

**mathematical method**

First of all let's expand this (2-i)(1+3i)(3+4i) = (2-i)(3 + 13i + 12i^2) = (2-i)(13i - 9) , remember that i^2 = -1 = 26i - 18 - 13i^2 + 9i = -5 + 35i magnitude = √(25 + 1225) = √1250 = 25√2

*August 16, 2016*

**math**

Their share of the profit should be proportional to the amount of their investment Total investment = 13000 Alex's share is 8000/13000 = 8/13 Ali's share is 5/13 So 5/8 = 2000/x , assuming Ali and Ally are the same person 5x = 16000 x = 3200 check: 2000 : 3200 = 5 : 8

*August 16, 2016*

**Math**

The distance between them is decreasing at a rate of 50 mph, (17+13) So in the last minute the distance to be covered is (1/60)(50) miles ----> recall, distance = rate x time = 5/6 of a mile

*August 15, 2016*

**math**

Don't become obsessed with formulas, just think it through. you want the distance around 1/2 of a circle = (1/2)(2π(30)) = 30π Then you must add the diameter, which would be 60 cm total = 30π + 60 which looks like πr + 2r

*August 15, 2016*

**Help on PreCalc**

As usual, make a sketch of a right-angled triangle and using Pythagoras, r^2 = 8^2 + 15^2 = 289 r = 17 π<α<3π/2 ----> α is in quadrant III sin α = -15/17 and cos α = -8/17 recall cos 2A = 1 - 2sin^2 A thus: cos α = 1 - 2sin^2 (α...

*August 15, 2016*

**Maths**

"1/3 of boys and 1/4 of girls." is not a complete sentence. What about the 1/3 of boys and 1/4 of girls ?

*August 15, 2016*

**Pre-calc**

tan2θ=7/11 ; π<2θ<3π/2 so 2Ø is in quadrant III and Ø is in quadrant II construct a right-angled triangle, with angle 2Ø, opposite side as 7, and adjacent side as 11 the hypotenuse is √170. Remember 2Ø is in ...

*August 13, 2016*

**Pre-calc**

As Steve and Damon pointed out to you earlier, sin(α−β) = sinαcosβ - cosαsinβ given: tanα=5/7 and sinα<0 , so by the CAST rule α must be in quadrant III since tanα = 5/7, by Pythagoras, the hypotenuse of our triangle ...

*August 13, 2016*

**Algebra**

So go ahead and simplify the expression that Steve gave you.

*August 12, 2016*

**math**

let the size of the cut-out be a square of side x inches base = (8-2x) by (11.75 - 2x) and the height is x x(8-2x)(11.75-2x) = 63.75 x(94 - 39.5x + 4x^2) = 63.75 94x - 39.5x^2 + 4x^3 - 63.75 = 0 don't know what method you know to solve a cubic, I ran it through Wolfram and...

*August 11, 2016*

**Calc**

let the angle between the two equal sides be Ø area = (1/2)(L)(L)sinØ , (you should know that formula) d(area)/dØ = (1/2)L^2 (-cosØ) , where L is a constant for a max of area (1/2)L^2(-cosØ) = 0 cosØ = 0 but of course cos 90° =0 ...

*August 11, 2016*

**Algebra**

Assuming that each way is 400 miles, (even though in Rome they wouldn't know what miles are, and would be using km.) let speed of plane in still air be x mph let speed of wind be y mph going with the wind: 5(x+y) = 400 ---> x + y = 80 going against the wind: 10(x-y) = ...

*August 11, 2016*

**precal**

x2 - 6x + 5y = -34 5y = -x^2 + 6x - 34 = -1(x^2 - 6x + 9 - 9) -34 = -(x-3)^2 + 9 - 34 y = (-1/5)(x - 3)^2 - 25/5 y = (-1/5)(x-3)^2 - 5 lots of algebraic typing ahead, so I will let you watch 4 great videos dealing with this topic by the remarkable Mr. Khan https://www....

*August 11, 2016*

**Maths**

roots of 4x^2-16x+15=0 are a and b, (for alpha and beta) by the properties of roots of a quadratic a+b = -(-16/4) = 4 ab = 15/4 new roots: a/b and b/a sum of new roots = a/b + b/a = (a^2 + b^2)/(ab) now a^2 + b^2 = (a+b)^2 - 2ab = 4^2 - 2(15/4) = 17/2 so sum of new roots = (17...

*August 11, 2016*

**Math**

My money is on Henry's solution

*August 11, 2016*

**Pre-calc**

That's not what you had originally. Glad you changed it, now my solution should make sense to you.

*August 11, 2016*

**Pre-calc**

The wording of your question makes no sense to me. Do you want csc(5π/6) as found on the unit circle? We have an ordered pair associated with (5π/6) , not csc(5π/6) I strongly suggest you print out one of the many unit circle diagrams available. Here is one of ...

*August 11, 2016*

**correction - Math**

easier way (and correct answer) : let the cost of a tie be $x cost of a shirt = $(x+50) 4x + 7(x+50) = 746 4x + 7x + 350 = 746 11x = 396 x = 36 Each tie costs $36, (and a shirt costs $86) expensive tastes!

*August 11, 2016*

**Math**

8 men mow 4 identical greens in 20 minutes 2 men mow 1 identical green in 20 minutes 6 men mow 1 identical green in 60 minutes

*August 11, 2016*

**Math**

2400 hectares of canola in 12 days using 4 machines 600 hectares of canola in 12 days using 1 machine 3600 hectares of canola in 12 days using 6 machines or time is directly proportional with the acreage and inversely with the number of machines T = k (A/M) given: 12 = k(2400/...

*August 11, 2016*

**Maths**

I don't see a quadrilateral bounded by only 3 sides.

*August 10, 2016*

**algebra**

Just translate the English to Math: let the height be x ft "the width is 3 times longer than the height" ---> width = 3x "the length is 9 times longer than the height" -----> length = 9x Now use the given to form your equation x(3x)(9x) = 64 27x^3 = ...

*August 10, 2016*

**algebra**

fix typo

*August 10, 2016*

**Math**

52728 = 3 x 2^3 x 13^3, and (2^3 x 13^3) is a perfect cube so dividing 52728 by 3 would leave a quotient of 17576 which is 2^3 x 13^3 or 26^3 thus the smallest such number as a divisor is 3 and the cube root of the quotient is 26

*August 10, 2016*

**maths**

In a parallelogram, adjacent angles must add up to 180° 4x-15 + 5x-3 = 180 I will let you finish it.

*August 10, 2016*

**Math**

sin Ø = 3/5 , so Ø could be in quadrants I or II make a sketch of the triangle and you should recognize the 3-4-5 right-angled triangle. the cosØ = 4/5 if Ø is in I and cosØ = - 4/5 if Ø is in II

*August 10, 2016*

**Math**

original fraction ---- x/(x+1) new fraction = (x-2)/(x-1) (x-1)/(x-2) + 4x/(x+1) = 5 times (x-2)(x+1), the LCD (x-1)(x+1) + 4x(x-2) = 5(x-2)(x+1) x^2 - 1 + 4x^2 - 8x = 5x^2 - 5x - 10 3x - 9 = 0 x = 3 original fraction is 3/4 check: new fraction = 1/2 1/(1/2) + 4(3/4) = 2 + 3...

*August 10, 2016*

**math**

total of pages ---- x 120 + .15x + .1x + 60 = x solve for x

*August 9, 2016*

**probability**

what is 360/(360+318) ?

*August 9, 2016*

**probability**

what is (61/100)(640) rounded to the nearest whole number ?

*August 9, 2016*

**probability**

use the concept that Bob showed you here: http://www.jiskha.com/display.cgi?id=1470754142

*August 9, 2016*

**Opt math URGENT**

RS = (1/16)(-6cosØ) I picked a random angle, Ø = 25 LS ≠ RS the equation is not true, thus we can't prove the identity

*August 9, 2016*

**Maths**

routine right-angled triangle trig x/3.8 = cos 65 x = 3.8cos 65° take over

*August 9, 2016*

**Math**

4x + 3.0 = -4x + 2.6 4x + 4x = 2.6 - 3.0 carry on, it is easy

*August 9, 2016*

**Math**

Start with the unit x x 1 x 6 1 -2 6 1, no way x 7 2 -1 7 2 , no way x 8 3 0 8 3 , not really a 3 digit number >b>1 9 4 ---- looks good 1 10 5 , no way

*August 9, 2016*

**Math**

"of" usually means multiplication , not subtraction, so you want (1/8)(12) = 12/8 = 3/2

*August 9, 2016*

**math**

smaller number --- x next consecutive number ---- x+1 3(1/(x+1)) - 1/x = 3/10 multiply each term by 10x(x+1), the LCM 30x - 10(x+1) = 3x(x+1) 30x - 10x - 10 = 3x^2 + 3x 3x^2 - 17x + 10 = 0 (x - 5)(3x - 2) = 0 x = 5 or x = 2/3 but our number was to be an integer, so x = 5 the ...

*August 9, 2016*

**Maths**

one number ---- x , the larger the other --- 14-x x(14-x) = 40 14x - x^2 = 40 x^2 - 14x + 40 = 0 (x-10)(x-4) = 0 x = 10 or x = 4 the two numbers are 10 and 4.

*August 7, 2016*

**Maths**

No typo, the solution is correct first case was 2 years ago 2nd case is 6 years from now what is the time difference? Husnain, I even checked to show you that answer is correct.

*August 6, 2016*

**Maths**

2 years ago: Susie---- x Ronald --3x 6 years from now: Susie = x+8 Ronald = 3x + 8 3x+8 = 2(x+8) x = 8 2 years ago, Ronald was 24 So now he is 26 check: ages now: Ronals --- 26 Susie ---- 10 6 years from now Ronald will be 32 Susie will be 16 Ronald is twice as old as Susie, ...

*August 6, 2016*

**ratio and proportions**

number of rabbits ---- x number of cats ------- 2x number of dogs ----- 3(2x) = 6x 6x - 10 = x 5x = 10 x = 2 so 2 rabbits 4 cats 12 dogs

*August 6, 2016*

**Math**

S(1) = 1/(1*2*3) = 1/6 S(2) = 1/6 + 1/(2*3*4) = 1/6 + 1/24 = 5/24 S(3) = 5/24 + 1/(3*4*5) = 5/24 + 1/60 = 9/40 Wolfram said: http://www.wolframalpha.com/input/?i=1%2F(1*2*3)+%2B+1%2F(2*3*4)+%2B+1%2F(3*4*5)+%2B+...+%2B+1%2F(n*(n%2B1)*(n%2B2))

*August 6, 2016*

**math**

−4≤2x+6<18 subtract 6 -10 ≤ 2x < 12 divide by 2 -5 ≤ x < 6 remember, only multiplication and division by a negative number will affect the inequality sign. Since I multiplied by +2, nothing happened.

*August 6, 2016*

**algebra**

let's assume you have 1/√(x+1) multiply top and bottom by √(x+1) 1/√(x+1) * √(x+1)/√(x+1) = √(x+1)/(x+1)

*August 6, 2016*

**math**

correct

*August 6, 2016*

**Algebra**

If you meant: (1/2)x(2x-4)^2 = (1/2)(x)( 2(x-2) )^2 = (1/2)(x)(2^2)(x-2)^2 = (1/2)(x)(4)(x-2)^2 = 2x(x-2)^2 ----> that answer was correct or 2x^3 - 8x^2 + 8

*August 5, 2016*

**Algebra**

smaller number ---- x "The larger of two numbers is 5 less than twice the smaller number" ---> 2x - 5 Now just translate: "The sum " ---> + "The sum of [four times the larger] and [twice the smaller number] ---> 4(2x-5) + 2x " is 100"...

*August 5, 2016*

**Incorrect Subject label - Maths**

discussed here: http://www.jiskha.com/display.cgi?id=1412345782

*August 5, 2016*

**ALGEBRA**

this has been answered

*August 5, 2016*

**A**

Once you see the pattern, listing 7 numbers in each case is a trivial problem. Option 1 - they tell you the pattern Option 2 - square the numbers Option 3 - double the previous number

*August 5, 2016*

**Math**

6 workers do 1 km in 4 days 1 worker does 1 k m in 4/6 or 2/3 days 4 workers do 1 km in 8/3 days 4 workers do 3 km in 3(8/3) or 8 days

*August 4, 2016*

**insight academy**

amount invested at 10% -- x amount invested at 12% ---- 12000 - x .10x + .12(12000 - x) = 1280 easy to solve for x

*August 4, 2016*

**Math**

you probably meant: A= (x+4)/(xsquared+9x+20) = (x+4)/((x+4)(x+5)) = 1/(x+5) , x ≠ -4 B = (3xsquared-9x)/(xsquared+3x-18) = 3x(x - 3)/((x+6)(x-3)) = 3x/(x+6) , x ≠ 3 clearly they are not equivalent I am sure you can handle the algebra from this point.

*August 3, 2016*

**math**

value = mt + 1500 when t = 4, value = 800 800 = 4m + 1500 4m = -700 m = -175 value = -175t + 1500 plug in t = 5 to find value

*August 3, 2016*

**someone please help me. - Precalc**

y=cos(x−5π/2) amplitude = 1 period = 2π If we had the simple curve y = cos x the quarter points would be (0,1) , (π/2, 0) , (π, -1), (3π/2 , 0) , and repeating at (2π, 1) but we shifted our basic cosine curve 5π/2 units to the right, so...

*August 3, 2016*

**Math**

It says f'(x) = 2x-1 for x ≤ 1, so x = 1 is included and valid for f'(x) to get f'(1) = 1 for x ≤ 1, f(x) = x^2 - x + c which is a parabola opening upwards, we don't know c but notice that when x = 1 , f(1) = c so it "ends" at (1,c) for x&...

*August 3, 2016*

**Math**

height --- 4.9 base --- 3.9 area = (1/2)base x height = ...

*August 3, 2016*

**Math Problem**

lots of "dogs and chicken" problems listed below in Related Questions. Take a look at some of them

*August 3, 2016*

**Math**

Think about where the zeros can come from 1! = 1 , 2! = 2 , 3! = 6 , 4! = 24, 5! = 120 <-- our first zero ..... 10! = 3628800 <-- our 2nd zero that is, a zero comes from a number ending in 2 multiplied by a number ending in 5, or by a number ending in 0 so the zeros ...

*August 3, 2016*