Saturday

September 20, 2014

September 20, 2014

Total # Posts: 27,130

**Math**

How about this pattern term(1) = 6 = 3(2^1) term(2) = 12 = 3(2^2) term(3) = 24 = 3(2^3) term(4) = 48 = 3(2^4) .... term(23) = .... = 3(2^23) term(n) = .....
*April 7, 2014*

**Math**

Q(t) = 200 (1/2)^(t/14.2) or Q(t) = 200(.5)^(.0704t) Q '(t) = (200/14.2) (.5)^(t/14.2) so when t = 21.5 Q ' (t) = (200/14.2) (.5)^(21.5/14.2) = 4.931 g/day
*April 6, 2014*

**algebra 2**

This produces an arithmetic series, where a = -5 and d = 8 sum(28) = (28/2)(-10 + 27(8)) = 2884
*April 6, 2014*

**Math**

I am sure you meant: Q(t) = 7000/(1 + 249 e^(-.6t) ) Q(10) = 7000/(1 + 249 e^(-.6(10) ) ) = appr 4328
*April 6, 2014*

**algebra 2**

so a = -12 , d = 5 sum(n) = (n/2)(2a + (n-1)d ) = (11/2)(-24 + 10(5)) = (11/2)(26) = 143 OR sum(n) = (n/2)(first + last) = (11/2)(-12 + 38) = 143
*April 6, 2014*

**algebra 2**

The famous mathematician Gauss, while he was in elementary school, notices the following 1+2+3+..+58+59+60 = (1+60) + (2+59) + (3+58) +.. (for a total of 30 of these pairs) = 30(61) = 1830
*April 6, 2014*

**MATH**

A polynomial must have a non-negative integer exponent. A and B contain square roots or exponents of 1/2 D: 11/(√x)^2 = 11/x or 11 x^-1 so none is a polynomial C: x - √11 yup, I would go with that one
*April 6, 2014*

**Algebra**

Did you mean: (2x+6)/(4x-8) ?? = 2(x+3)/(4(x-2)) = (x+3)/(2(x-2) or (x+3)/(2x - 4)
*April 6, 2014*

**Math**

I would consider it a "combination" , assuming that the order that you choose the appetizers should not matter Number of ways = C(4,2) x C(5,1) = 6x5 = 30
*April 6, 2014*

**Calculas**

P(4) = 100(4) - 3(16)ln(4) = .. I assume you have a calculator to get appr 333.46
*April 4, 2014*

**Calculus Help Please!!!**

dy/dx = 8x(1/2)(x-x^2)^(-1/2) (1 - 2x) + 8(x-x^2)^(1/2) = 4(x-x^2)^(-1/2) [ x(1-2x) + 2(x-x^2) ] = (4/√(x-x^2) ( x - 2x^2 + 2x - 2x^2) = (4/√(x-x^2) (3x - 4x^2) = 0 for a max/min 3x - 4x^2 = 0 x(3 - 4x) = 0 x = 0 ----> looks like it will yield a min x = 3/4 ---&...
*April 4, 2014*

**typo - Calculus Help Please!!!**

only valid for 0 ≤ x ≤ 1
*April 4, 2014*

**Calculus Help Please!!!**

only valid for 90 ≤ x ≤ 1 http://www.wolframalpha.com/input/?i=y+%3D+%3D+8x%28√%28x+−+x%5E2%29%29+%2C+0+%3C+x+%3C+1
*April 4, 2014*

**Algebra**

But you wanted to use the formula ... x = (-4 ± √100)/2 = (-4 ± 10)/2 = (-4+10)/2 or (-4-10)/2 = .....
*April 4, 2014*

**Algebra**

put it into standard form of a quadratic ... x^2 + 4x - 21 = 0 how nice that it factors .... (x+7)(x-3) = 0 so x = ... or x = ....
*April 4, 2014*

**percentages/word problem**

costprice = 80 after first markup, SP = 80(1.5) after 20% mark down = 8(1.5)(.8) another 15% markup = 8(1.5)(.8)(1.15) final markdown of 60% = 8(1.5)(.8)(1.15)(.4) = 8(.552) = 4.42
*April 3, 2014*

**Calculus1**

let the width of the beam be 2w and the depth be 2d S = k(2w)(4d^2) = 8k w(d^2) I drew a circle and incribed a rectangle with the defined dimensions. Notice the diagonal is 12 Construct a righ-angled triangle, with sides w, d, and hypotenuse 6 w^2 + d^2 = 36 d^2 = 36-w^2 in S...
*April 3, 2014*

**Math - Algebra2**

f(x)=3x+2 , g(x)=3/x^2+2 , h(x)=sqrt(x-2) (f∘g)(-5) to me means: f (g(x) ) so f(g(5)): g(-5) = 3/27 = 1/9 f(1/9) = 3(1/9) + 2 = 1/3 + 2 = 5/3 (f∘g)(-5) = 5/3 so the others the same way
*April 3, 2014*

**Precalculus**

w = -i - 2j describes the vector (-1,-2) so it the same way I showed you in the similar problem of unit length. YOu can do it in your head to get (-1/√5 , -2/√5)
*April 3, 2014*

**Algebra**

for any quadratic of the form y = ax^2 + bx + c the x of the vertex is -b/(2a) so for yours ... x of the vertex is -184/(-32) = 5.75 so it took 5.75 seconds, plug that into your original function to find the maximum height.
*April 3, 2014*

**Pre calculus**

correct notice you can check that the magnitude is 1 magnitude = √( (1/√2)^2 + (-1/√2)^2 ) =√( 1/2 + 1/2) = √1 = 1
*April 3, 2014*

**Pre calculus**

for any unit vector in the direction of (a,b) .... find the length of the vector = √(a^2+b^2) now divide each component by that magnitude to get (a/√(a^2+b^2) , b/√(a^2+b^2) or you could write it as (1/√(a^2+b^2) (a,b) apply this to your vector, let me ...
*April 3, 2014*

**algebra**

welcome
*April 3, 2014*

**algebra**

multiply each term by 2x(x+1) 6x - 2(x+1) = x(x+1) 6x - 2x - 2 = x^2 + x x^2 +3x + 2 = 0 (x-1)(x-3) = 0 x = 1 or x = 3
*April 3, 2014*

**Calculus1**

it would be a combination of the chain rule and the product rule, doing it as a single power the way I did it was easier as a product rule - chain rule for that term ..... x√x = x x^(1/2) derivative: x (1/2) x^(-1/2) + (1)x^(1/2) = x/(2√x) + √x = x/(2√x...
*April 3, 2014*

**Calculus1**

yes, of course, silly me, the exponent on the last one was 3/2
*April 3, 2014*

**Calculus1**

I would rewrite as h(x) = 3x^(1/2) - x^(3/2) h ' (x) = (3/2) x^(-1/2) - (2/3) x^(1/2) = 3/(2√x) - (2/3) √x
*April 3, 2014*

**Algebra**

it will hit the ground when the height h(t) = 0 -16t^2 + 144 = 0 16t^2 = 144 t^2 = 144/16 = 9 so t =√9 = 3 after 3 seconds
*April 3, 2014*

**Pre calculus**

welcome
*April 3, 2014*

**Pre calculus**

PS-3PQ = (-10,4) - 3(2,5) = (-10,4) + (-6,-15) = (-16,-11) magnitude is √((-16)^2 + (-11)^2) = √377
*April 3, 2014*

**Algebra**

since you want the height horizontally from the starting height, and that height was 5.4 metres, -.06x^2 + 9.6x + 5.4 = 5.4 the 5.4 drops out, so x(-.06x + 9.6) = 0 x = 0 , the starting time or x = 9.6/.06 = 160 it will land after 160 m
*April 3, 2014*

**Geometry**

let the chord AB = 2x then the diameter = 2x+2 or the radius = x+1 This allows me to draw a right-angled triangle with sides x and 9 and hypotenuse x+1 (x+1)^2 = x^2 + 9^2 x^2 + 2x + 1 = x^2 + 81 2x = 80 x = 40 AB = 80 check: diameter = 82 is 41^2 = 40^2 + 9^2 ? LS = 1681 RS...
*April 2, 2014*

**Algebra II**

rowing speed in still water ---- x mph speed of current ------------- 2 mph time to go 50 miles with the current = 50/(x+2) time to go 25 miles against current = 25/(x-2) the two times are the same, so ... 50/(x+2) = 25/(x-2) 50x - 100 = 25x + 50 25x = 150 x = 6 speed in still...
*April 2, 2014*

**slope**

y = 3x - 7 straight line with slope of 3 and y-intercept of -7 http://www.wolframalpha.com/input/?i=y+%3D+3x+-+7
*April 2, 2014*

**Pre-calc**

What are we doing with this hyperbola ?
*April 2, 2014*

**Math help**

look back at your previous post of this
*April 2, 2014*

**Math**

let the slant height of one side be h then using (1.2)base x height 1980 = (1/2)(35.4)h h = 3960/(35.4) = 111.8644 = appr 111.86 m this can't be. According to the given dimensions on the webpage, the base is about 35 by 35 and the height is 21.6 m, for a slant height of 27...
*April 2, 2014*

**calculus**

let the two equal width be x let the single side by y xy = 600 y = 600/x cost = 20y + 30x = 20(600/x) + 30x d(cost)/dx = -12000/x^2 + 30 = 0 for a min of cost 30 = 12000/x^2 x^2 = 400 x = 20 the two equal sides are 20 yds each, and the long side is 600/20 = 30 yds.
*April 2, 2014*

**Word problem**

the x of the vertex is -b/(2a) = -184/(-32) = 5.75 seconds plug that into the function h(5.75) = 16(5.75^2) + 184(5.75) + 20 = 549 ft
*April 2, 2014*

**Finance**

monthly rate = .041/12 = .00341666.. let the effective annual rate be i 1 + i = (1 + .00341666..)^12 1+i = 1.0417783 i = .0417783 or appr 4.18%
*April 2, 2014*

**PRE CALC**

using the standard notation: term(20) = a + 19d = 27 and a = -11 -11 + 19d = 27 19d = 38 d = 2 the common difference is 2 check: term(2) = a+19d =-11 + 19(2) = -11+38 = 27
*April 2, 2014*

**calculus**

I see that C(1990) is given as 271.9 What are you asking?
*April 2, 2014*

**Equations**

did it, look back
*April 2, 2014*

**trig**

after 1 hours, one ship has gone 25 km, the other 15 km make a sketch, let the distance between them be x straigh-forward case of the cosine law x^2 = 25^2 + 15^2 - 2(25)(15)cos 60° = .... you do the arithmetic. (I got appr 21.8 km)
*April 2, 2014*

**Algebra Question~!**

To be a factor, the division has to be exact, that is, the remainder must be zero works that way with numbers, works that way in algebra.
*April 2, 2014*

**Calculus Help Please!!! Check**

looks like you are using Newton's Formula for Cooling properly.
*April 2, 2014*

**Derivatives**

write it as: G(t) = 5200 (1+12e^(-.52t)^-1 G ' (t) = -5200(1+12e^(-.52t) )^-2 (-.52)(12)e^(-.52t) = + 32448 e^(-.52t) / (1+12e^(-.52t) )^2 I got a positive instead of your negative.
*April 2, 2014*

**kaylah - math**

kaylah, you can't draw a triangle with 2 sides parallel !!
*April 2, 2014*

**math**

Can you draw a 4-sided figure with 2 lines parallel ?
*April 2, 2014*

**Equation help 2 questions**

You state the equation as a function, so to speak of real number solutions makes no sense. There are an infinite number of solutions, any ordered pair satisfying the equation would be one. You probably want the solution to -4x^2 + 7x - 8 = 0 in both cases, it depends on the ...
*April 2, 2014*

**Math**

t(1) = 1/3 t(n) = 3term(n-1) , n>1
*April 2, 2014*

**Calculus Help**

I can add more rats!! last step: dx/dt = -6( csc^2 (π/3)) (-π/3) = -6((4/3)(-π/3) = 24π/9 km/min = 8π/3 km/min (which is Steve's answer)
*April 2, 2014*

**Calculus Help**

At a time of t min after the plane passed over the tracking telescope, let the horizontal distance be x km Let the angle of elevation be Ø Make a sketch, I get cot Ø = x/6 x = 6cotØ dx/dt = -6 csc^2 Ø dØ/dt when Ø = π/3 and d&...
*April 2, 2014*

**Calculus Help Please!!!**

given : dr/dt = 40 cm/s A = πr^2 dA/dt = 2π r dr/dt case 1: when s = 1, r = 40 dA/dt = 2π(40)(40) = 3200π cm^2/sec case 2: when s = 3, r = 3(4) = 120 cm dA/dt = 2π(120)(40) = 9600π cm^2/sec case 3: ... your turn .....
*April 2, 2014*

**math**

multiples of 5 and 8 from 1 to 110 : either 40 or 80 so prob of your event = 2/100 = 1/50
*April 2, 2014*

**algebra 2**

subtract them : 30y^2 - 96x = 192 5y^2 = 32 + 16x back into the first: 16x^2 - (32+16x) = 64 16x^2 -16x - 96 = 0 x^2 - x - 6 = 0 (x-3)(x+2) = 0 x = 3 or x = -2 if x = 3, 5y^2 = 32+48 = 80 y^2 = 16 y = ± 4 if x = -2 5y^2 = 32-32 = 0 y = 0 so we have 3 points: (-2,0) , (3...
*April 2, 2014*

**Math**

ignore the 2nd part of my answer to the above, the numbers don't even match. I cut and pasted from a previous solution but the numbers were not even the same Also note that even though 263 is a solution, it is one of an infinite number. But it said to find "a number&...
*April 2, 2014*

**Math**

look up "Chinese Remainder Theorem" and you will find many pages for this kind of problem You will have to know how to do arithmetic in "modular arithmetic" , and this forum is not suitable to teach you that. I just worked out the above problem using that ...
*April 2, 2014*

**Equation help**

you must have a typo, since all your terms are positive. Your rock will continue to rise higher and higher. I was expecting the square term to be negative. so I will assume that -.04x^2 + 1.3x + 56 = 0 (y is zero when it hits the ground) times -100 4x^2 - 130x - 5600 = 0 x = (...
*April 2, 2014*

**math**

number of boys --- 2x number of girls --- 5x after 12 new boys number of boys = 2x+12 girls , still 5x (2x+12)/(5x) = 4/9 18x + 108 = 20x 108 = 2x x = 54 So now the number of boys = 2x+12 = 108+12 = 120
*April 2, 2014*

**math**

your data just has to be entered here http://davidmlane.com/hyperstat/z_table.html
*April 2, 2014*

**Math**

forgot the link http://www.jiskha.com/display.cgi?id=1329034595
*April 1, 2014*

**Math**

looks like yours, just input 20 instead of the 60
*April 1, 2014*

**Algebra II**

number from A ---- x number from Bx+6000 solve for x: .04x + .03(x+6000) = 880
*April 1, 2014*

**Math**

did it here .... http://www.jiskha.com/display.cgi?id=1396401662 give your posts a bit of time. You reposted this with only about 20 minutes in between. If tutors are online they may be answering somebody else's question while yours is waiting.
*April 1, 2014*

**Combinations Algebra Readiness**

you should know these w definitions nCr = n!/( r!(n-r)! ) nPr = n!/(n-r)! 6C3 = 6!/(3!3!) = 20 6P4 = 6!/2! = 360 On most scientific calculators both of these functions are built-in on mine they are found below the 5 - key and the 6-key to do 6C3 enter 6 2ndF 5 3 = to get 20 ...
*April 1, 2014*

**Algebra**

√(y+3) - 4 = 5 what about it? are we solving for y? √(y+3) = 9 square both sides y+3 = 81 y = 78 test it.
*April 1, 2014*

**Math!!!**

4/100 = x/80 100x = 320 x = 3.20 or take .2($4) = $ .80 after discount, cost = $ 4.00 - .80 = $3.20
*April 1, 2014*

**Calculus Help Please!!!**

done http://www.jiskha.com/display.cgi?id=1396400942 are you switching names???
*April 1, 2014*

**Calculus Help Please!!!**

Use the product rule to get f ' (t) = -(t^2 - 32)/√(64-t^2) = 0 for a local max/min t^2 = 32 t = ±4√2 f(±4√2) = 0 f(-1) = -1√63 f(8) = 8(√0) = 0 there you go, you got your f(t)'s what do you think? Here is your graph, notice ...
*April 1, 2014*

**MATH UGH WORD PROBLEM**

capacity of tank = π r^2 h = π(100^2)(40) = 400000π number of gallons = 7.5(400000π) = appr .....
*April 1, 2014*

**Calculus Help!**

see http://www.jiskha.com/display.cgi?id=1396388805
*April 1, 2014*

**not - trigonometry**

Why are you calling this trig ? assuming his first deposit is NOW end of 1st year: 1000(1.06) + 1000 = 2060 end of 2nd year: 2060(1.06) + 1000 = 3183.60 ... end of 5th year: .......... = 6637.09 fill in the rest using your calculator
*April 1, 2014*

**algebra**

first one: add them, 2y = 6 y = 3 sub into the 2nd: (could have used the 1st, makes no difference) 2x - 3 = 1 2x = 4 x = 2 so x=2, y=3 do the 2nd one by adding them, follow my example
*April 1, 2014*

**math..help again**

look back at your previous post of this same question
*April 1, 2014*

**Math- urgent**

1st number --- x 2nd number --- y "The second of two numbers is five more than the twice first." ---> y = 2x+5 "the sum of the numbers is 44" ---> x+y = 44 x+y = 44 x + (2x+5) = 44 x + 2x + 5 = 44 3x = 39 x = 13 1st is 13, 2nd is 31 check: is 31 five ...
*April 1, 2014*

**Math**

area of whole thing is 120x60 = 7200 ft^2 so half of that is 3600 ft^2 make a sketch showing the first run area of 1st run = 120x4 + 120x4 + 52x4 + 52x4 = 1376 leaving 2224 make a sketch of the remaining rectangle which is 112 by 52 area of 2nd run = 112x4+112x4+48x4+48x4 = ...
*April 1, 2014*

**Math**

ummmhhh, how many sides does a hexagon have ?
*April 1, 2014*

**trig**

I assume you want the distance traveled along the hypotenuse, d, then sin30° = 5000/d d = 5000/sin30 d = ... if you want the horizontal distance traveled , x tan30 = 5000/x x = 5000/tan30 = ...
*April 1, 2014*

**Urgent Calc Help!!! Thanks!**

f ' (x) = x( xe^((−x^2)/98)(-2x/98) + e^((−x^2)/98) = e^((−x^2)/98) ( -x^2/49) + 1) = 0 for a max/min -x^2/49 +1 = 0 x^2 = 49 x = ± 7 evaluate f(7) f(-7) f(-6) f(14) and determine which is the largest and which is the smallest
*April 1, 2014*

**Calculus**

f ' (t) = -8sin t + 2(4 cos t) = -8sint + 8cost = 0 for a max/min 8sint = 8cost sint/cost = 1 tant = 1 t = 45° or 225° or t = π/4 , t = 5π/4 -->(outside our domain) so evaluate f(0) f(π/4) f(π/2) and determine which is the largest and which ...
*April 1, 2014*

**Calculus Help Please!!!**

so it the same way you were just given in your previous post. Let us know what you got
*April 1, 2014*

**Calculus Help Please!!!**

looks like we both messed up in the f(x) calculations should be f(4) = 2(64) - 3(16) - 72(4) + 7 = -201 f(-3) = 2(-27) - 3(9) - 72(-3)+7 = 142 end-values: f(-4) = 2(-64) - 3(16)( - 72(-4) + 7 = 119 f(5) = 2(125) - 3(25) - 72(5) + 7 = -178
*April 1, 2014*

**Calculus Help Please!!!**

f ' (x) = 6x^2 - 6x - 72 = 0 for a local max/min x^2 - x - 12 = 0 (x-4)(x+3) = 0 x = 4, or x = -3 f(4) = 2(64) - 3(16) - 72(4) + 7 = -201 f(-3) = 2(-27) - 3(9) - 72(-3)+7 = 115 end-values: f(-4) = 2(-64) - 2(16)( - 72(-4) + 7 = 135 f(5) = 2(125) - 3(25) - 72(5) + 7 = -178 ...
*April 1, 2014*

**math**

I gave it to you ... instead of y I have "cost" instead of x I have "n" y = mx + b <-----> cost = (1/10)n + 5
*April 1, 2014*

**math**

I will assume that your given ordered pair (10,6) is of the type (number , cost), then cost - 6 = (1/10)(number -10) cost = (1/10) number -1 + 6 cost = (1/10)n + 5 so if n = 25 cost = (1/10)(25) + 5 = 7.5 units of cost (you gave no units)
*April 1, 2014*

**calculus and vectors**

Add the 2 equations ... 6x + y = 6 y = 6-6x let x = 0 , y = 6 2(0) + 4(6) + z = 5 --> z = -19) we have a point (0,6,-19) on the line of intersection let x = 1, y = 0 2(1) + 4(0) + z = 5 --> z = 3 and (1,0,3) is another point on that line So a direction vector of that ...
*April 1, 2014*

**Algebra II**

just plug in your value: 24.2 = √(19.6 h) √h = 24.2/√19.6 h = (24.2/√19.6)^2 = 29.88 m or I know from physics that h = 4.905 t^2 gives you the height from which an object was dropped after t seconds , and v = 9.81 t gives you the velocity after t ...
*April 1, 2014*

**maths geometry**

let the distance of the shorter chord to the centre be x x^2 + 15^2 = 25^2 x^ = 400 , x = 20 let the distance between the longer chord and the centre by y y^2 + 24^2 = 25^2 y^2 = 49 , y = 7 so x+y = 27 the chords are 27 cm apart
*April 1, 2014*

**Algebra**

the way you typed it would be r = (2√5) L or did you mean r = 2√(5L) major difference between the 2 formulas, please clarify.
*March 31, 2014*

**math**

let the 3 numbers be a , b, and c, in order of size, c is the largest a+b+c = 36 c = 2a b = (a+c)/2 = (a+2a)/2 = 3a/3 back into the first a+b+c = 36 a + 3a/2 + 2a = 36 times 2 2a + 3a + 4a = 72 9a = 72 a = 8, then c = 16, and b = 12 Our 3 numbers are 8, 12, and 16 (all ...
*March 31, 2014*

**Math**

your answeres are correct so far. for the increasing/decreasing part, find dy/dx I got (-c((ax+b) + a(cx+d))/(cx+d)^2 = (ad - bc)/(cx + d)^2 since the denominator is always ≥ 0 we only have to look at the top for the function to increase , dy/dx > 0 ad - bc > 0 for...
*March 31, 2014*

**Algebra 1**

Didn't know baskets were worth 4 point, did you mean 2 or 3 points? I will assume that. number of 2-pointers ---x number of 3-pointers --- 9 2x + 3(9-x) = 22 2x + 27 - 3x = 22 x = 5 so 5 two-pointers and 4 three-pointers check" 5(2) + 4(3) = 22
*March 31, 2014*

**math**

Same structure as the one I just did for you. Try it, let me know what you got.
*March 31, 2014*

**math**

amount(1.03)^5 = 5(125000) I got $ 539,130.49
*March 31, 2014*

**statistics**

plug in your data here .... http://davidmlane.com/hyperstat/z_table.html to get .4013
*March 31, 2014*

**Math**

prob(spade facecard, then king) = (3/52)(4/52) = 3/676
*March 31, 2014*

**math**

3sin = 1.2 sinØ = .4 (set your calculator to RAD) Ø = .41152 or π-.41152 which is 2.73008 but you wanted from 0 to 4π so add a period , or 2π, to each of the above answers Ø = .41152 , 2.73008 , .6947, and 9.01326
*March 31, 2014*

**trig**

I drew a circle, and a vertical radius of 12 m In 40 s, it rotates 360°, so in 5 sec it rotated 45° let the vertical position from the centre be y cos45 = y/12 y = 8.485 m so he is 12-8.85 or appr 3.5 m high after 5 seconds
*March 31, 2014*

**Math**

just translate the English into Math, 4x - 6 = 2x + 4 then solve for x
*March 30, 2014*

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