Thursday

October 8, 2015
Total # Posts: 31,225

**Math**

Even though a formula to solve a cubic equation exists, nobody in their right mind would use it http://www.math.vanderbilt.edu/~schectex/courses/cubic/ The first thing I usually do is to try the factor theorem look for factors of 6 which might work try x = ±1, ±2...
*September 5, 2015*

**math**

you know it must look like 3xy also 3+x+y = 5x y = 4x - 3 if x = 1, y = 1 , number is 311 , but none are the same if x = 2, y = 5, number is 325 , looks ok if x = 3, y = 9 , number is 339, but none can be the same if x = 4, y = 13, not possible the number is 325
*September 5, 2015*

**math complex number**

I get (-4 - i)/13 (-2+i) / (3-2i) = (-2+i) / (3-2i) * (3+2i)/(3+2i) = (-6-4i + 3i - 2i^2)/(9 - 4i^2) = (-6 - i + 2)/(9+4) = ( -4 - i)/13
*September 5, 2015*

**Algebra**

looks like a typo, where is c ?
*September 5, 2015*

**Algebra**

sometimes it helps if you just relate the problem to a specific numerical case. e.g. supposed you were asked how far a car going 60 km/h would go in 3 hours. the answer is clearly 180 km What did we do to get 180 ? we multiplied 3 by 60 so if the time is y hours instead of 3 ...
*September 4, 2015*

**Math**

tree : shadow = 12 : 6 = 2 : 1
*September 4, 2015*

**Math**

This is a sneaky question, f(x) = (x^2+3x+2)/(x+2)*tan(π*x) = (x+1)(x+2)/(x+2) tan(πx) = (x+1)tan(πx) the vertical asymptote is caused by the tan(πx) part, recall that tan90° is undefined, and 90° = π/2 radians or (1/2)π so if x = 1/2 we ...
*September 4, 2015*

**Algebra**

no, the correct choice is B , which says in a simplified way that xy = yx notice the two factors are switched
*September 4, 2015*

**math**

Using the factor theorem , I tried x = ±1, ±2, ±4, and it worked if x = -4 so by synthetic division: 4x^3 + 32x^2 + 79x + 60 = (x-4)(4x^2 + 16x + 15) = (x-4)(2x+5)(2x+3) (x-4)(2x+5)(2x+3)=0 x = -4, or x = -5/2, or x = -3/2 and sure enough -5/2 + (-3/2) = -...
*September 4, 2015*

**MATH**

better form would be to place the equal sign in front of each new line You also have errors -3(x + 3)- 2(x + 4) = -3x - 9 - 2x - 8 = -3x - 2x - 9 - 8 = -5x - 17
*September 3, 2015*

**math**

I cannot decipher your text on my Mac - instead of creating the symbols, state them in words e.g 56 degrees for 56° in your second question, where is X ? Is it on some line?
*September 3, 2015*

**Algebra**

5x+2y according to your definition of x and y shows me that each adult ticket costs $5 and a student's ticket costs $2. for 5x + 2y = 220 the x-intercept is 44 , the y=0 the y-intercept is 110, the x = 0 Meaning: if no students show up, then the number of adult that went ...
*September 3, 2015*

**algebra**

assuming that letters may be repeated, and no words formed are restricted .... number of plates = 3x26x26x26x26 = 3(26^4) = ...
*September 3, 2015*

**math**

your are in quad II drop a perpendicular to the x-axis and draw your right-angled triangle cosØ = x/r secØ = r/x remember : r^2 = x^2 + y^2 = (-5)^2 + 5^2 = 50 r = 5√2 secØ = 5√2/-5 = -√2
*September 3, 2015*

**Math**

just use your decimal let x = .232323... 100x = 23.232323... subtract them: 99x = 23 x = 23/99 so 5.2323.... = 5 23/99 or 518/99 check with your calculator to verify it to be correct.
*September 3, 2015*

**Alg 2**

You did not indicate what your choices are
*September 3, 2015*

**algebra 2**

ahhh, so you mean 2|3x-5| - 8 = 8 then 2|3x-5) = 16 |3x-5| = 8 3x-5 = 8 or -3x+5 = 8 3x = 13 or -3x = 3 x = 13/3 or x = -1
*September 3, 2015*

**Mat**

210= 3*7*2*5
*September 3, 2015*

**Math**

list them, then add them up
*September 3, 2015*

**Math**

follow my previous solution, except we cannot start with a 0
*September 3, 2015*

**Math**

possible numbers: single digits: 1 2 3 double digits 12 13 23 21 31 32 triple digits: 123 132 213 231 312 321 Can you add them up ?
*September 3, 2015*

**Math**

I will assume that the interest is 7.5% per annum compounded quarterly. (The interest period must coincide with the payment period for our formula to work) i = .075/4 = .01875 n = 20 payment = p p(1 - 1.01875^-20)/.01875 = 38000 I get p = 2296.02
*September 3, 2015*

**raj english school**

one rotation covers 63π cm so 200 rotations will cover .... ?
*September 3, 2015*

**Geometry**

I meant to say: in a vertical line (early morning senior moment)
*September 3, 2015*

**Geometry**

radius = 3 (easy to see since the given point and the centre lie in a horizontal line) C = 2πr = 6π units
*September 3, 2015*

**math**

no, you multiplied instead of dividing 15 - 2 1/3 = 12 2/3, (you had 12 3/4) "He cut the remaining cloth into equal pieces" -- assuming you meant 2 equal pieces , it should have said that. There could have been 3 equal pieces, or 45 equal pieces , or .... 12 2/3 &...
*September 3, 2015*

**typo - Math**

oops, 1/5 hr = 12 minutes, not 20 minutes so 1 hour, 12 minutes
*September 2, 2015*

**Math**

mechanic' rate --- 1/2 assistant's rate --- 1/3 combined rate = 1/2 + 1/3 = 5/6 time at combined rate = 1/(5/6) = 6/5 hrs or 1 hour 20 minutes
*September 2, 2015*

**math**

Your period is not correct If the temp is 36° at 4:00am and 56° at 4:00pm you only have 1/2 a period. Doesn't the temperature have to come back down at 4:00am so you should have 2π/24 or π/12 so try: Temp = -10 cos (πt/24) + 46
*September 2, 2015*

**math! please help!**

This looks almost identical to the one I answered here http://www.jiskha.com/display.cgi?id=1359417542
*September 2, 2015*

**Math**

I assume that x ---> 1 Use Hopital's Rule = limit 500x^499/1 = 500(1) = 500
*September 2, 2015*

**Maths**

rigorous method: 1/9 = 20/180 3/2 = 270/180 4/5 = 144/180 19/20 = 171/180 , 180 being the LCD so what do you think? (of course the answer was obvious, since 3/2 is the only fraction greater than 1)
*September 2, 2015*

**MATH**

2^8 x 16^3 x 64 = 256 x 4^6 x 4^3 = 4^4 x 4^6 x 4^3 = 4^13
*September 2, 2015*

**MATH**

= (1/x)^-1 = x
*September 2, 2015*

**MATH**

taking your typing at face-value, since you have no brackets N = a-b^a - b, for the given values = 2 - 2^2 - 2 = 2 - 4 - 2 = -4
*September 2, 2015*

**math**

looks like you are multiplying a term by 2 to get the next one, so .....
*September 1, 2015*

**Math**

12 = 4*3 16 = 4*4 20 = 4*5 24 = 4*6 = 4*2*3 perfect squares come in pairs of equal factors so we need 4*4*25*9 = 3600
*August 31, 2015*

**Math**

looks to me like n^2 - 6 = 5770 n^2 = 5776 n = √5776 = 76 76 rows
*August 31, 2015*

**Math, trigonometry**

did you make your sketch ? looks like tan 4.25° = 47/x x = 47/tan4.25° calculator time ...
*August 31, 2015*

**additional maths**

I don't know if you are the same person, but this question is a cut-and-past of http://www.jiskha.com/display.cgi?id=1422453360 areas are measured in cm^2 , not cm^3 I cannot understand 2 cm2 ´ s -1
*August 30, 2015*

**Math**

for each rotation, the wheel travels the circumference of the circle, so find the circumference of the circle for the distance of one rotation, and ... - how many rotations do you have ?
*August 30, 2015*

**Maths**

The model had measurement of 4/25 m by 6/25m = .16 m by .24 m = 16 cm by 24 cm area = (16)(24) cm^2 = 384 cm^2 or area of actual room = 400 cm by 600 cm area = 240000 cm^2 but areas are proportional to the square of the sides, so divide by 25^2 or 625 to get 384 cm^2
*August 30, 2015*

**Math**

first of all, I am sure you meant y=1/2x-2 Secondly, is it y=(1/2)x-2 ? , the way you typed it or y=1/(2x)-2 ? or y=1/(2x-2) ? See how critical those brackets are ?
*August 30, 2015*

**equation**

You must be referring to the 2nd term of (3^-x)^4 + (3^-x)^-3 = 81 notice in the previous line it was 3^(3x) which is (3^x)^3 or (3^(-x))^-3 Steve substituted 3^x, I substituted 3^-x, our equations reflect that No, logs will not work here, since you have to take the log of a ...
*August 30, 2015*

**equation**

I did similar what Steve did, and agree with him Steve asked you to improve your typing of the equation, but this does not change things. I will assume you meant: 9^(-2x) + 3^(3x) = 81 which becomes 3^(-4x) + 3^(3x) = 81 (3^-x)^4 + (3^-x)^-3 = 81 let 3^-x = t so we have: t^4+ ...
*August 30, 2015*

**Trigonometry/ please help!**

oops, forgot the 7, thanks Steve
*August 29, 2015*

**Trigonometry/ please help!**

you are right, S = 4 cos (πt/2) does not pass through the origin. Perhaps you meant, where does it cross the t - axis? in that case 4cos(πt/2) = 0 we know cos(π/2) = 0 so πt/2 = π/2 t = 1 or t = -1 we also know that the period of your function is 2&#...
*August 29, 2015*

**Calculus**

looks good to me http://www.wolframalpha.com/input/?i=plot+y+%3D+xsecx%2C+y+%3D+%28%CF%80%E2%88%9A2%2F4+%2B+%E2%88%9A2%29x+%2B+%CF%80%E2%88%9A2%2F4+-+%28%CF%80%E2%88%9A2%2F4+%2B+%E2%88%9A2%29%28%CF%80%2F4%29
*August 29, 2015*

**Calculus**

y = x secx , point is (π/4 , π√2/4) dy/dx = x secx tanx + secx = secx(x tanx + 1) so at the given point: slope = √2( (π/4)(1) + 1) = π√2/4 + √2 so using y = mx + b π√2/4 = (π√2/4 + √2)(π/4) + b solve ...
*August 29, 2015*

**alegbra 2**

from first principles, the directrix is y = 7 let P(x,y) be any point then PF = PD, where D is the vertical distance from P to the directrix √( (x-6)^2 + (y-1)^2 ) = √(x-x)^2 + (y-7)^2 ) square and expand x^2 - 12x + 4 + y^2 - 2y + 1 = y^2 - 14y + 49 x^2 - 12x - 44...
*August 29, 2015*

**Calculus**

y = √x (x^3 + 1) dy/dx = x(1/2) (3x^2) + (1/2)x^(-1/2) (x^3 + 1) = (1/2)(x^(-1/2)) (6x^3 + x^3 + 1) = (7x^3 + 1)/(2√x) you are correct, but you need brackets around the denominator, or else it is only divided by 2
*August 29, 2015*

**Math**

One mile = 5280 ft = 5280(12) inches each rotation of the smaller wheel = 32π inches number of rotations = 4264.5(5280)(12)/32π = appr 2,687,716 each rotation of the larger wheel = 54π inches number of rotations = 4264.5(5280)(12)/(54π) = appr 1,592,721 ...
*August 29, 2015*

**Math**

I agree with your method and with your answer
*August 29, 2015*

**math**

look at all the variations of your question in the Related Questions below
*August 29, 2015*

**math**

amount added ..... x L solve for x, .6(80) + 0.0x = .5(80+x) 48 = 40 + .5x x = 16
*August 29, 2015*

**maths**

missing information
*August 29, 2015*

**algebra**

I will assume that letters can be repeated. So for your first letter you can only choose from 3 letters. Number = 3x26x26 = ....
*August 28, 2015*

**calculus**

SA = 4πr^2 d(SA)/dt = 8πr dr/dt subbing in our values d(SA)/dt = 8π(3)(-2) = -48π you differentiated volume, it asked to find the rate of change of the surface area. So you need to differentiate surface area
*August 28, 2015*

**Math**

The odds of rolling two dice for a sum greater than 9 are 6:30, or 1 : 5 so the probability of greater than 9 is 1/6 The probability of less than or equal to 9 is 5/6 Make sure to understand that "odds" and "probability" are not the same thing. I don't ...
*August 28, 2015*

**Math**

The concept of odds is slightly different from probablity the odds in favour of some event = prob of the event happening : prob of the event NOT happening so, prob of direct hit = .2 prob of no direct hit = .8 odds in favour of no direct hit = .8 : .2 = 8:2 = 4 : 1
*August 28, 2015*

**Math**

I will assume you meant: (x^2-y^2)/(x-y)^2 , those brackets are important = (x+y)(x-y)/(x-y)^2 = (x+y)/(x-y) , x≠y
*August 28, 2015*

**Pre-algebra**

Irrational means "not a ratio" or not a fraction. the fact that you wrote it as 7/8 , .......
*August 27, 2015*

**Math**

I will assume that point C is supposed to be on the curve y = x^2 and that point (1,1) stays constant. label the points: A(1,1), B(0,b) and C(c,c^2) , since y = x^2 slope of AB = (b-1)/-1 or 1 - b slope of AC = slope of AB = (c^2 - 1)/(c-1) then (c^2 - 1)/(c-1) = 1-b c^2 - 1...
*August 27, 2015*

**pre-calculus**

the 15 would be the number of units of height he would climb every minute You don't say what units, but I would assume h(t) is in metres. the graph would be increasing, that is, it would rise to the right. h(1000) makes no physical sense even though you get a mathematical ...
*August 27, 2015*

**Math**

let the distance be d km time on first trip = d/320 time on return trip = d/480 d/320 + d/480 = 5 the LCD is 960 3d/960 + 2d/960 = 5 5d/960 = 5 d/960 = 1 d = 960 (in Montreal they would use km and km/h, not miles and mph)
*August 27, 2015*

**ALBEBRA**

simplest way to explain: the mosaic is 3 ft by 5 ft or 36 inches by 60 inches for a total area of 2160 square inches each time covers 6x12 or 72 square inches number of tiles = 2160/72 = 30 tiles or since the length is 60 inches, we can stand 10 tiles in the first row. it is ...
*August 27, 2015*

**Math**

the outcomes you want are (3,6) or (6,3) there are 36 possible outcomes, so the prob(of your event) = 2/36 = 1/18
*August 27, 2015*

**calculus**

amount = c (2^(t/10)), where t is in minutes and c is the initial amount so when covered by 50% .... .5 = 1 (2^(t/10) take log of both sides log .5 = log 2^(t/10) log .5 = (t/10)log 2 t/10 = log .5/log2 = -1 t = -10 So it was covered to 50% 10 minutes ago, or at 11:50 am when ...
*August 27, 2015*

**Algebra**

rate of old pump = tank/7 rate of new pump = tank/5 combined rate = tank/7 + tank/5 = (5tank + 7tank)/35 = 12tank/35 combined time = tank/(12tank/35) = 35/12 = 2 11/12 hours = 2hours and 55 minutes
*August 27, 2015*

**math**

If you entered it the way you typed it above, I noticed you left out the variable for time it should be y = -1020/7 x + 1020 or try : y = (-1020/7)x + 1020 checking, for now, x = 0, x = 0 + 1020 = 1020, checks! for 7 years from now, x = 7 y = (-1020/7)(7) + 1020 = 0 , checks!
*August 27, 2015*

**Geometry**

multiply each term by 3 3by + 2 = 3c 3by = 3c - 2 divide both sides by 3b y = (3c-2)/(3b)
*August 27, 2015*

**Algebra**

you did not finish at the end 3x(x^2-9y^2/(3x(4x+12y)) is correct, notice the brackets at the denominator = 3x(x-3y)(x+3y)/((3x)(4)(x+3y)) = (x-3y)/4 , x ≠ 3y looks like choice #1, if you had included the brackets
*August 27, 2015*

**math**

we know that 2lw + 2lh + 2wh = 184 or their hint: lw + lh + wh = 92 there would be an infinite number of solutions, e.g. let w = 4, l = 8, then 4(8) + 8h + 4h = 92 12h = 60 h = 5 so length = 8, width = 4, and height = 5 check: 4*8 + 4*5 + 8*5 = 92 let w = 1, h = 6 l + 6l + 6...
*August 27, 2015*

**equation on tangent of a curve need help**

In x^2.y^3+y^2.x^4+4x^2-14=0 I will assume you are using the "." as a multiplication symbol Usually we use the * symbol x^2(3y^2)dy/dx + y^3(2x) + y^2(4x^3) + x^4(2y)dy/dx + 8x = 0 dy/dx(3x^2 y^2 + 2x^4 y) = -2x y^3 - 4x^3 y^2 -8x dy/dx = (-2x y^3 - 4x^3 y^2 - 8x)/(...
*August 27, 2015*

**math analysis**

Just like in numerical fractions, you will need a common denominator , which would be (x-5)(x-3) so we get ( (x+3)(x-3) + 5(x-5) )/((x-5)(x-3)) = (x^2 - 9 + 5x - 25)/(x^2 -8x + 15) = (x^2 + 5x - 34)/(x^2 - 8x + 15)
*August 24, 2015*

**Maths**

s + r = 494 ---> s = 494-r (3/5)r/(s-57) = 2/3 9r/5 = 2s - 114 use substitution 9r/5 = 988 - 2r - 114 9r/5 = 874 - 2r times 5 9r = 437 - 10r r = 230 s = 264
*August 21, 2015*

**Math**

why not just take the √ of both sides as it stands (x-2)^2 = 49 x-2 = ± 7 x = 2 ± 7 = 9 or -5 you had x^2 - 4x - 45 = 0 which would have factored to (x-9)(x+5) = 0 x = 0 or x = -5
*August 12, 2015*

**Calculus**

draw a right-angled triangle (side view) mark the base as 80, and the height of the balloon as h a) you want to know how fast the balloon is receding, so we are talking about how fast the hypotenuse is changing. let the hypo be x x^2 = 80^2 + h^2 2x dx/dt = 0 + 2h dh/dt, but ...
*August 12, 2015*

**Calculus**

http://www.jiskha.com/display.cgi?id=1439263714
*August 12, 2015*

**algebra 2**

I find that changing everything to sines and cosines usually works well for these type of problems unless you recognize one of the standard formulas. LS = sin^2 x (1 + cos^2 x/sin^2 x) = sin^2 x (sin^2 x + cos^2 x)/sin^2 x , forming a common denominator = sin^2 x (1/sin^2 x...
*August 11, 2015*

**@ Steve - Math**

I ain't touching that one :)
*August 11, 2015*

**Maths**

Make a sketch. the line from the centre hits the chord at its midpoint and you have a right-angled triangle. You can use Pythagoras. r^2 = 3.3^2 + 5.6^2 = 42.25 r = √42.25 = 6.5
*August 11, 2015*

**math**

The way your question is worded makes no sense You must have meant this: done by Steve last year http://www.jiskha.com/display.cgi?id=1397894767
*August 11, 2015*

**eua high school**

surface area of a graph???
*August 11, 2015*

**Calculus**

done, look at your previous post
*August 11, 2015*

**calculus**

to be at rest, v = 0 4t^2 - 1 = 0 4t^2 = 1 t^2 = 1/4 t = 1/2 let the displacement be s s = (4/3)t^3 - t + c assume that when t = 0 , s=0 , then c =0 s= (4/3)t^2 - t when t = 1/2 s = (4/3)(1/4) - 1/2 = 1/3 - 1/2 = -1/6 the object is 1/6 m to the "left" of O
*August 11, 2015*

**Calculus**

y = 1 - cos^2 x y = 1 - (cos x)^2 dy/dx = -2cosx (-sinx) = 2 sinx cosx or sin (2x)
*August 11, 2015*

**yale high school**

your number when divided by 4 leaves a remainder of 3 when divided by divided by 5, leaves a remainder of 2 numbers which fit the first case: 7 11 15 19 23 27 31 35 39 numbers which fit the 2nd case: 7 12 17 22 27 the least number would be 7, but I have a feeling they are ...
*August 11, 2015*

**math**

your equation factors to (w-4)(2w + 13) = 0 so w = 4 or w = -13/2, which makes no sense so the width is 4 and the length is 2(4) + 5 or 13
*August 11, 2015*

**please help urgent**

For your second, the 15-year plan i = .0775/12 = .00645833.. n = 15(12) = 180 p( 1 - 1.00645833^-180)/.006458333 = 300000 I got p = 2823.83 you had the same, good job As to your last question, you cannot just add up the payments. e.g. a payment of $500 made today does not have...
*August 10, 2015*

**please help urgent**

I will do the first, you do the 2nd i = .085/12 = .00708333.. n = 30(12) = 360 payment = p PV = p(1 - (1+i)^-n)/i 300000 = p(1 - 1.00708333^-360)/.007083333) 300000 = p(130.0536..) p= 2306.74
*August 10, 2015*

**Maths**

I don't know your notation of 100/-
*August 10, 2015*

**Urgent math**

This is an arithmetic series where a = 40000 , d=1900 you want sum(10) sum(10) = (10/2)(2(40000) + 9(1900)) = 485500 What you found is how much he made in the 11th year.
*August 10, 2015*

**Calculus**

make a sketch let the distance of the man from the lamp-post be x let the length of his shadow be y by ratios: 5.5/y = 10/(x+y) 5.5x + 5.5y = 10y 5.5x = 4.5y times 10 55x = 45y 11x = 9y 11 dx/dt = 9 dy/dt 11(8) = 9 dy/dt dy/dt = 88/9 ft/s or 9 7/9 ft/s --> rate at which the...
*August 10, 2015*

**Math**

Did you post this question under the name of Fay? http://www.jiskha.com/display.cgi?id=1439188422 a(1) = 1 a(2) = 3 a(1) + 6 = 3(1) + 6 = 9 a(3) = 3 a(2) + 6 = 3(9) + 6 = 33 a(4) = 3 a(3) + 6 = 3(33) + 6 = 105 a(5) = 3 a(4) + 6 = 3(105) + 6 = 321
*August 10, 2015*

**Calculus**

What about it ?
*August 10, 2015*

**Math**

It should be clear to you that the 37.313 is the number of quarter years, and if I divide that by 4 I would get years 37.313../4 = 9.33 years rounded to 2 decimal places
*August 10, 2015*

**Math**

i = .075/4 = .01875 1. n = 4(3) = 12 amount = 3000(1.01875)^12 = 3749.15 2. 3000(1.01875)^n = 6000 , where n is the number of quarter years 1.01875^n = 2 take logs of both sides and use use of logs n log 1.01875 = log 2 n = log 2/log 1.01875 = appr 37.313 = 37.313../4 or appr ...
*August 10, 2015*

**Algebra**

7% = .07 , not .7 like you had That was your major mistake. a) equation: n(t) = 1900 e^(.07t) b) if 2005 ---> t = 0 then 2010 ---> t = 5 n(5) = 19000 e^(.07*5) = 26962 I don't understand how you could possible think that 5 foxes would be correct. there were 19000 ...
*August 10, 2015*