Friday
August 22, 2014

Posts by Reiny


Total # Posts: 26,966

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

Algebra
y-5 = -5x + 10 5x + y = 15
March 30, 2014

math
We will need to find the sides angle P = 180 - 60 - 75 = 45° let PQ=x , QR = y , PR = z x/sin75 = y/sin45 = z/sin60 let's assign an arbitrary value of y = 1 to our smallest side using x/sin75 = 1/sin45 we get x = .1.366025 using 1/sin45 = z/sin60 z = 1.224745 so sum of...
March 30, 2014

Math
ways to choose 5 of the 6 multiple choices = C(9,5) = 126 number of ways to choose 2 of the 6 essay questions = C(6,2) = 15 number of ways to answer the test = 126x15 or 1890 ways
March 29, 2014

Finance
I have now answered 2 of these kind of questions for you. Exactly where are you finding difficulties with these? Do you know the 4 basic formulas we have to use for these ?
March 29, 2014

Finance
PV = 10000(1 - 1.08)^-10)/.08 + 20000(1 - 1.08^-30)/.08 (1.08)^-10 = 171391.45 or pretend you are gettting 20,000 for 40 years - the 10,000 for the first 10 years = 20000(1 - 1.08^-40)/.08 - 10000(1 - 1.08^-10)/.08 = 171391.45
March 29, 2014

Finance
150000 =PAY( 1 - 1.07^-20)/.07 solving for PAY, I got $ 14,158.94 Balance owing after 7 years = 150000(1.07)^7 - 14158.94( 1.07^7 - 1)/.07 = $ 118.335.46
March 29, 2014

math
I will assume you meant: log3 (2x + 5) = 1 then 2x+5 = 3^1 2x = -2 x = -1 If otherwise, let me know
March 29, 2014

survey math 140
Number of ways to select 5 of 19 is C(19,5) = 19!/(5!14!) = 11628 most calculators have that function built-in look for something like nCr
March 29, 2014

algebra
James, I gave you a detailed solution yesterday for the same question on the assumption that your symbol was supposed to be ≥ You later told me that it was to be ≤ So why don't you just switch all the conditions e.g. all the domain that worked before, now will ...
March 29, 2014

Math
I am guessing that P(number < 2) is supposed to mean probability that the number is less than 2 What number ???? Are you tossing a die ? confirm
March 28, 2014

calcules
let base be x by x let the height be y x^2 y = 8 y = 8/x^2 SA = base + 4 sides = x^2 + 4xy = x^2 + 4(8/x^2) = x^2 + 32/x d(SA)/dx = 2x - 32/x^2 = 0 for a minimum of SA 2x = 32/x^2 2x^3 = 32 x^3 = 16 x = cuberoot(16) = appr 2.52 then y = 1.26 the base is 2.52 by 2.52 and the ...
March 28, 2014

Algebra 2
same idea as before, factor first, then divide, restrict what you divided by Again, I am putting in the brackets, they are extremely important here h(x)=(x^2-9)/(x^2-4x+3) = (x+3)(x-3)/(x-1)(x-3)) = (x+3)/(x-1) , x ≠ 3
March 28, 2014

Algebra 2
I have a feeling you meant: (49X^6+7X^7)/(28X^8) take out a common factor = 7x^6( 7 + x)/(28x^8) now divide = (7+x)/(4x^2) now we divided top and bottom by a variable. If that variable is zero, we just divided by zero, which is a mathematical no-no. so we have to state a ...
March 28, 2014

algebra
I have a strong feeling you meant (x-4)(x+2)/( (x-3)(x+5) ) ≥ 0 I good and fast way is to look at the graph of y = (x-4)( (x+2)/(x-3)(x+5) ) http://www.wolframalpha.com/input/?i=y+%3D+%28x-4%29%28x%2B2%29%2F%28%28x-3%29%28x%2B5%29%29 It shows the graph to be above the x-...
March 28, 2014

Geometry
You are missing one of the dimensions of the floor, its length Once you have that, Cost = 105 ( 33 * 1/2 * ??)/27 units of money where ?? in your length we divide by 27 since there are 27 cubic feet in 1 cubic yard If the concrete is sold in whole cubic yards, you will have to...
March 28, 2014

ALGEBRA
the t of the vertex of your parabola is -b/(2a) = -20/-32 = 5/8 at t = 5/8 h = -16(25/64)+20(5/8) + 6 = 12.25 nope!
March 28, 2014

math
avg rate of change = (23500 - 8750)/(8 = ...
March 27, 2014

Math
treat it as two ordered pairs (t, c) where t is temperature and c is consumption so we have (90,220) and (76, 178) slope = (220-178)(/(90-76) = 42/14 = 3 so: c-220 = 3(t-90) c = 3t - 270+220 c = 3t - 50 check: if t = 90, c = 270-50 = 220 if t = 76, c = 228 - 50 = 178
March 27, 2014

Math
no, 26x^2 ≠ x√26 Whatever made you think so. let x = 4 26(4^2) = 26*16 = 416 xV26 = 4√26 = appr 20.4 is 416 = 20.4 ???? However, you could write 26x^ as (x√26)^2
March 27, 2014

Math
Imagine "opening up" a cylinder, what would you get? 2 equal circles + a rectangle whose length is the circumference of the circle and whose height is the height of the cylinder. so SA = 2π(6^2) + 2π(6)(20) = 72π + 240π = 312π = appr 980 No ...
March 27, 2014

Math
I assume you pick a card, then throw the die primes from 1-10 : 2,3,5,7 , so 4 of them primes on a die: 2 3 5, so 3 of them prob(2 primes) = (4/10)(3/6) = 1/5 prob(not 2 primes) = 4/5 odds in favour of getting two primes = (1/5) : (4/5 = 1 : 4
March 27, 2014

2nd question - math help!!
(x+y)^2-x-y = (x+y)^2 - (x+y) = (x+y)(x + y - 1)
March 27, 2014

math help!!
To make it easier to see, let 2x^2 - x = a so you have 2a^2 - 3a - 9 = (a-3)(2a+3) put the original back in = (2x^2 - x - 3)(4x^2 - 2x + 3) = (x + 1)(2x - 3)(4x^2 - 2x + 3)
March 27, 2014

Math
cosine law .... 5.4^2 = 6.2^2 + 3.6^2 - 2(6.2)(3.6)cosR cosR = 22.24/44.64 = .4982.. R = 60.1°
March 27, 2014

Math
direct application of the sine law: x/sin41 = 96/sin71 x = 96sin41/sin71 = ....
March 27, 2014

Calculus Help Please!!!
According to Newton's Law of Cooling T(t) = roomtemp + (37 - 20)e^(-kt) , where t is the time in hours and k is a constant so we get two equations: 32.5 = 20 + 17e^(-kt) ---> 12.5 = 17e^(-kt) and 30.3 = 20 + 17e^(-k(t+1)) ---> 10.3 = 17e^(-kt - k) divide them: 115/...
March 27, 2014

Algebra
did you try factoring both expressions? They factor quite easily. Then divide out the common factor, don't forget to state the restriction.
March 27, 2014

trig
Not sure what notation you are using when you say "blowing in at 53° " is North your 0° and you are going clockwise, or is 0° your positive x - axis and you are going counterclockwise ?
March 27, 2014

Calculus
just using ln a^b = b ln a ln (243^3/5 *32^4/5) = ln ( (3^5)^(3/5) * (2^5)^(4/5) ) = ln ( 3^3 * 2^4) = ln (27*16) = ln(432) 1/5 ln (243^3 * 32^4) = ln [ (243^3 * 32^4) ^(1/5) ] = ln (243^(3/5) * 32^(4/5) ) = .... = ln(432)
March 27, 2014

Calculus
I agree with Damon's "huh" since ln (243^3/5 *32^4/5) = 1/5 ln (243^3 * 32^4)
March 27, 2014

FINANCE
choice A: pay 3100(.85) or 2635 now choice B: pay 12 payments of 270 present value of the 12 payments at a monthly rate of i = 270( 1 - (1+i)^-12)/i= 2635 hard to solve, let Wolfram do it for us (I changed the i to x, since Wolfram thinks i = √-1 ) http://www....
March 26, 2014

math 2
let E(x,y) be your point use ratios ... for the x: (x-3)/(11-3) = 3/8 8x-24 = 24 8x = 48 x = 6 for the y: (y-4)/(3-4) = 3/8 8y - 32 = -3 8y = 29 y = 29/8 E is (6,29/8)
March 26, 2014

math
y - 6 = .5x - 3.5 y = .5x - 3.6 + 6 y = .5x + 2.5
March 26, 2014

math
slope of AB = 4/-2 = -2 so slope of new line = +1/2 new line: y-6 = (1/2)(x-7) expand and doctor it up any way you want.
March 26, 2014

argggh - Calculus
messed up in my expansion volume should have been 4x^3- 120x^2 + 800x and V' = 12x^2 - 240x + 800 = 0 3x^2 - 60x + 200=0 to get x = 4.23
March 26, 2014

Calculus
First things first: width --- s length ---- 2s 2s^2 = 800 s^2 = 400 s = 20 so the piece of metal is 20 by 40 let the side of the square to be cut out be x so the width is 20-2x the length is 40-2x the height is x Volume = x(20-2x)(40-2x) = 2x^3 - 120x^2 + 800x d(Volume)/dx = ...
March 26, 2014

Algreba
What about it ?
March 26, 2014

Calculus
you should have recalled that sin (-x) = -sinx so that sin(-.1) could not have been positive. did you mean -.1 ?
March 26, 2014

Math
slope of new line must be -2 so y =-2x + b plug in the given point (2,-7) -7 = -2(2) + b -3 = b y = -2x - 3
March 26, 2014

Calculus
yes v(t) = h ' (t) = -16t + 5 so v(0) = -16(0) + 5 = 5
March 26, 2014

math
times 8 8B = 3(A-10) 8B = 3A - 30 8B+30 = 3A A = (8B+30)/3
March 26, 2014

Math
divide the fist equation by 2 to get y = 9x now plug that into the second: 9x - 6 = 2x 7x = 6 x = 6/7 then y = 9(6/7) = 54/7 x = 6/7 y = 54/7
March 26, 2014

math
I suspect that your equation is C = 6u^2 v (usually they would not separate factors of 6 and 2 like you did, and would have C = 12uv instead) Please confirm.
March 26, 2014

Math
prob(2dimes) = (8/14)(7/13) = 4/13
March 26, 2014

Math
consider the equation of the circle with centre (1,2) and radius 10 Its equation is (x-1)^2 + (y-2)^2 = 100 (7, 10) satisfies that equation, (7-1)^2 + (10-2)^2 = 100 6^2 + 8^2 = 100 36+64 = 100 100=100 so it is (7,10)
March 26, 2014

College Calculus
let Ø be the angle between them the angular velocity of the minute hand = 2π/60 rad/min = π/30 rad/min the angular velicity of the hour hand = 2π/(12(60)) or π/720 rad/min then, so dØ/dt = (π/30 - π/720) rad/min dØ/dt = 23&#...
March 26, 2014

Math
looks like a combination recursion let term(n) be the nth term, term(1) = 2 if n is odd: term(n) = 3term(n-1) if n is even: term(n)= term(n-1) - 2 so the next terms are: 26, 78, 76, 228, 226, 678 .....
March 26, 2014

integer Math
Since they gave the answer as 7 , I am taking a guess that they wanted √52
March 26, 2014

Math
x( 1.07^27 - 1)/.07 =25000 x(74.483823..) = 250000 x = $ 3356.43
March 26, 2014

Precalculus II
don't you just love Wolfram http://www.wolframalpha.com/input/?i=plot+sec%5E2%28x%29%2B+3+tan%28x%29%3D5%2C+-2π+%3C+x+%3C+2π
March 26, 2014

math
Steve, that is really scary.
March 26, 2014

math
period of first = 2π/(12π) = 1/6 period of 2nd = 2π/(18π) = 1/9 1/3 is a factor of both, so the period = 1/3 verification: http://www.wolframalpha.com/input/?i=10+sin%2812+pi+t%29%2B4+cos%2818+pi+t%29
March 26, 2014

Finance
300( 1 - 1.01^-n)/.01 = 2000 300(1 - 1.01^-n) = 20 1 - 1.01^-n = 1/15 14/15 = 1.01^-n ln both sides and use rules of logs ln 14 - ln15 = -n ln 1.01 n = (ln 15 - ln 14)/ln 1.01 = 6.934 appr 7 months of course I could have used log 15 etc. and obtained the same result.
March 26, 2014

math
Who makes up these questions or what kind of strange paint is this? To paint a ceiling of that size should take about 1/2 gallon ( I know, I have too much time on my hand)
March 26, 2014

Math
number of adults --- A number of kids ----- C A + C = 35 12A + 7C = 315
March 25, 2014

calcules
Just noticed that both Damon and I answered a very similar question in the first of the Related Questions below http://www.jiskha.com/display.cgi?id=1268848081 I suggest you print it out , and change the numbers, and units.
March 25, 2014

math
solve 2 = e^(.07t) hint: take ln of both sides and use your log rules remember ln e = 1
March 25, 2014

math
what is 48000( 1.0105)^40 ?
March 25, 2014

Trigonometry
tan Ø = -√3 I know that tan 60 = +√3 and Ø could be in II or in IV in II , Ø = 180-60° = 120° or 2π/3 in IV, Ø = 360-60 = 300° or 5π/3
March 25, 2014

Calculus
let the number be x, and the sum as stated be S S = x^2 + 1/x dS/dx = 2x - 1/x^2 = 0 for a max/min 2x = 1/x^2 2x^3 = 1 x^3 = 1/2 x = (1/2)^(1/3) or the cube root of 1/2
March 25, 2014

Math
Brady, after all that work, you blew the final answer x+3x+6x = 180 10x=180 x = 10 but I called the angles x, 3x, and 6x so the angles are 18° , 54° , and 108° and of course 108° is the largest angle
March 25, 2014

Math
let the angles be x , 3x and 6x x + 3x + 6x = 180 take over ....
March 25, 2014

Grade 12 Calculus
I hope your function looks something like this: R(x) = (5000 - 100x)(30 + x) = 150000+ 5000x - 3000x - 100x^2 = -100x^2 + 2000x + 150000 this is a standard parabola opening dowwards , so it will have a maximum the x of the vertex is -b/(2a) = -2000/-200 = 10 So there should be...
March 25, 2014

Trigonometry
if sinx = -2/√5 in III y = -2, r = √5 , by Pythagoras, x^2 + 4 = 5 x = -1 in III cosx = -1/√5 tanx = sinx/cosx = (-2/√)/(-1/√5) = 2 sin 2x = 2sinxcosx = 2(-2/√5)(-1/√5) = 4/5 cos 2x = cos^2 x - sin^2 x = 1/5 - 4/5 = -3/5 tan 2x = 2tanx...
March 25, 2014

math
spent on perches --- x litter -------------- x -326 litter and perches combined = 2x - 326 nesting = 2(2x-326) 2x-326 + 2(2x - 326) = 4050 should be relatively easy to solve for x I get x = 838
March 25, 2014

Algebra 2
help with what? you didn't ask a question. your function simplifies to ... d(x) = 54x^10/(24x^8) = 4x^2 / 9 surely that wasn't your question, was it ?
March 25, 2014

MATH
so 2 + 4 + 8 + 16 + ... = 178 sum(n) = a(r^n - 1)/(r-1) 2(2^n - 1)/1 = 178 2^n - 1 = 89 2^n = 90 I know 2^6 = 64 2^7 = 128 2^8 = 256 So I agree with your answer , at the end of 7 you only have 128 but you need 178 so it must be the 8th month how did they come up with 10? ...
March 25, 2014

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