Saturday
December 3, 2016

Posts by Reiny

Total # Posts: 36,897

calculus need help studying now
a) I suggest expanding this rather than using the product rule y = (x^2 - 4x + 4)(x-7) = x^3 - 11x^2 +32x - 28 y ' = 3x^2 - 22x +32 y '' = 6x - 22 = 0 for a point of inflection x = 22/6 = 11/3 <------ there is your error y = (11/3-2)^2 (11/3-7) = (25/9)(-10/3...
November 28, 2016

Math Question
x^2+y^2-7x=12-4y x^2 - 7x + 49/4 + y^2 + 4y + 4 = 12 + 49/4 + 4 (x - 7/2)^2 + (y+2)^2 = 113/4 = ?113/2 you had that so the centre is (7/2 , -2) and the radius is ?113/2 which is appr 5.315 set you compass at appr 5.3 units, and with the above centre, draw your circle
November 28, 2016

Math
looks like you are just dividing your input by 10 y = x/10
November 28, 2016

math
Usually the "length" of a rectangle is greater than its "width", but anyway..... let the length be x yds then the width is x+15 yds x(x+15) = 100 x^2 + 15x - 100 = 0 (x - 5)(x + 20) = 0 x = 5 or x = -20, the latter is not possible the length is 5 and the ...
November 28, 2016

Math (please check my answer)
2 angles and the contained side of one triangle are the same as 2 angles and the same contained side of another, so ASA makes them congruent.
November 28, 2016

MATH @Damon @ms. Sue
The assumption we have to make is that the velocity is a linear function of the time .... So we have two ordered pairs (3,53) and (6,62) slope = (62-53)/(6-3) = 3 using the point (3,53) v-53 = 3(t-3) v-53 = 3t - 9 3t - v = - 44 or y = 3t + 44 should be easy to plot for 3 < ...
November 28, 2016

Math
younger brother --- x years Martha ----------- 2x years x + 2x = 36 carry on
November 28, 2016

Math
speed of current ---- x mph distance traveled each way ---- d miles time with the current = d/(6+x) time against the current = d/(6-x) d/(6-x) = 2d/(6+x) divide by d 1/(6-x) = 2(6+x) 6+x = 12 - 2x 3x = 6 x = 2 state your conclusion.
November 28, 2016

Math
salmon's rate of swimming --- x mph let rate of current be y mph 15/(x+y) = 3 3x+3y=15 ---> x+y=5 15/(x-y)=5 5x - 5y = 15 ----> x - y = 3 add those two equations: 2x = 8 x = 4 , then y = 1 state your conclusion
November 28, 2016

algebra
typo error in 90 c + 180 + 130 c = 4 c^2 + 80 c should be : 90 c + 1800 + 130 c = 4 c^2 + 80 c ---> c^2 - 35c - 450 = 0 (c - 45)(c + 10) = 0 c = 45 or a negative city speed was 45 mph
November 27, 2016

YT host subscribe now!!
Bro subscribe to the alex jones channel my man!
November 27, 2016

Business Math
i = .06/12 = .005 n = 20(12) = 240 PV = 50,000 paym = ?? paym( 1 - 1.005^-240)/.005 = 50,000 payment = $358.22 after 7 years: balance of mortgage = 50000(1.005)^84 - 358.22(1.005^84 - 1)/.005 = $38,737.12 Since the current value is 90,000 but they still owe 38,737.12 the ...
November 27, 2016

Math
"Determine the initial amount of the substance to the nearest 10th of an hour" HUH, since when is an amount of something measured in units of time?? (I will just ignore that part of the question) N = 8 e^(-6t) initial --- t=0 N = 8 e^0 = 8 mg <----- the initial ...
November 27, 2016

Math
let each of the equal sides be x cm A = (1/2)x^2 dA/dt = x dx/dt we know dA/dx = -5 cm^2 /s dx/dt = -5/x H^2 = x^2 + x^2 = 2x^2 H = ?2 x dH/dt = ?2 dx/dt = ?2(-5/x) so when x = 10 dH/dt = -5?2 /10 = -(1/2)?2 cm/s or appr -.707 cm/s
November 27, 2016

Algebra
number of dimes ---- x number of nickels ---- 2x + 1 value of coins: 10x + 5(2x+1) = 165 10x + 10x + 5 = 165 take over
November 27, 2016

math
http://www.jiskha.com/display.cgi?id=1480267024
November 27, 2016

Math
the way you typed it .... -5 + ?-50/10 = -5 + 5?2 i/10 = -5 + (?2/2) i what you probably meant: (-5 + ?-50)/10 = (-5 + 5?2 i)/10 = -1/2 + (?2/2) i
November 27, 2016

Emma
We solve equations, you don't have an equation if you meant: evaluate (?6+i)(?6-1) = 6 - ?6 + ?6i - i I have a strong feeling you meant: (?6+i)(?6-i) = 6 - i^2 , but i^2 = -1 = 6+1 = 7
November 27, 2016

Algebra
y = kx given: x=3, y=10 10 = k(3) k = 10/3 so y = (10/3)x when x = 6 y = (10/3)(6) = 20
November 27, 2016

precalcalculus
I assume you are familiar with the tradional way of identifying the information given about a triangle, such as ASA, SAS, SSS and SSA use "cosine law" for SAS and SSS use "sine law" for ASA and SSA #1 - a case of ASA --> a side contained between two ...
November 27, 2016

precalculus
There are several question of your type in the Related Questions section below
November 27, 2016

precalculus
Vague question. are you converting an equation or a point with rectangular coordinates?
November 27, 2016

Maths
For any number, there are 10 possible digits for the unit place, one of those is the 2. so prob(your event) = 1/10
November 27, 2016

Algebra
compare: http://www.jiskha.com/display.cgi?id=1480210517
November 26, 2016

Algebra
find the vertex of the parabola. The t of the vertex tells you when it reached the maximum height, the h tells you what that height is.
November 26, 2016

Math
equation: y = 100 (2)^(t/3.2) .. .. to get 450 bacteria 450 = 100 (2)^(x/3.2) 4.5 = 2^(x/3.2) take log of both sides and use log rules (x/3.2)log 2 = log 4.5 x/3.2 = log 4.5/log2 x = 6.944 hrs. or appr 7 hours
November 26, 2016

precalculus
How does this post differ from this one? http://www.jiskha.com/display.cgi?id=1480198638
November 26, 2016

PreCalc
let f(x) = 2x^3+x^2-8x+3 f(1) ? 0 f(-1) = -2+1+8+3 ? 0 f(3) ? 0 f(-3) ? 0 f(3/2) = 0 , yeahhhh, 2x-3 is a factor by long division, 2x^3+x^2-8x+3 = (2x-3)(x^2 + 2x -1) the quadratic has roots of x = -1 ± ?2 looking at the graph of y = 2x^3+x^2-8x+3 -1-?2 < x < -1+?...
November 26, 2016

Algebra
let the distance from Seattle to wilderness be x miles x/420 + x/300 = 6 times 2100 the LCM 5x + 7x = 12600 x = 1050 miles
November 26, 2016

Trigonometry
look at the cos^-1 (x/3) construct a triangle with base of x and hypotenuse of 3 by Pythagoras: r^2 = x^2 + y^2 3^2 = x^2 + y^2 y^2 = 9 - x^2 y = ?(9-x^2) so we want the tangent tan (cos^-1 x/3) = opposite/adjacent = ?(9-x^2)/3
November 26, 2016

precalculus
(3(cos(5pi/4)+i sin (5pi/4) ) )^8 = 3^8(cos 8(5?/4) + i sin 8(5?/4)) = 6561( cos 10? + i sin 10?) = 6561( 1 + i(0) ) = 6561 B (3-3i)^6 let z = 3-3i, so we want z^6 r = ?(9 + 9) = ?18 = 3?2 plot (3,-3) which is in IV, so Ø = 315° or 7?/4 z = 3?2(cos 7?/4 + i sin 7?/4...
November 26, 2016

precalculus
I checked the first 4, they were ok you seem to know what you are doing.
November 26, 2016

Trigonometry
a) isn't arcsin(sin(?)) the inverse of itself? so 13?/16 b) and c) same thing, except by definition arcsin( ..) will give you the smallest positive angle so arccos(cos(-?/18) = ?/18 d) arcsec(-?2) the angle Ø so that secØ = -?2 or cosØ = (-1/?2) &...
November 26, 2016

precalculus
a) ok b) (i-j)-(18i+27i) = -17i - 28j c) (5i-5j)-(30i+54j) --> you did 5u - 5v instead of 5u-v
November 26, 2016

pre calculus
250 pounds at 45° ---> (250cos45, 250sin45) 130 pounds at -60° ---> (130cos(-60), 130sin(-60) ) Resultant = (250cos45, 250sin45)+(130cos(-60), 130sin(-60) ) = (125?2, 125?2) + (65 , -65?3) = ( 125?2 + 65 , 125?2 - 65?3) = appr (241.7767 , 64.1934) maginitude...
November 26, 2016

Discrete Math
if you meant: x^1 + x^2 + x^3 + 2x^4 + x^5 = 68 there are none http://www.wolframalpha.com/input/?i=solve+x+%2B+x%5E2+%2B+x%5E3+%2B+2x%5E4+%2B+x%5E5+%3D+68
November 26, 2016

pre calculus
checking for right-angled triangle: is 100^2 = 55^2 + 85^2 ? NO so let's find the smallest angle by the cosine law: 55^2 = 100^2 + 85^2 - 2(100)(85)cosØ cosØ = 14200/17000 = .83529.. Ø = 33.35..° , (I stored it for accuracy on my calculator So area...
November 26, 2016

pre calculus
u=<0,-4>, v=<-2,-8> a) 2v+u = <-4,-16) + <0,-4) = <-4, -20> b) 5u - v = <0,-20> - <-2,-8) = <2, -12> c) do this one the same way
November 26, 2016

Mathmatics help please
clearly 25 and 15
November 26, 2016

Maths help asap please
3c-7 > 5c+4 3c - 5c > 4+7 -2c > 11 c < -11/2 or c < -5.5 so the smallest integer that is a solution is c = -6 check: if c = -6, -18 - 7 > -30+4 -25 > -36 , true! if c = -5 -15-7> -25+4 -22 > -21 , false
November 26, 2016

Math
subtract 2 from each part, and you are done -3<x+2<3 -3-2 < x+2-2 < 3-2 -5 < x < 1 ---> ( x lies between -5 and 1 )
November 26, 2016

Math
nothing wrong with that you could just use the trig-vector notation resultant = (10cos60,10sin60) + (20cos120,20sin120) + (30cos180,30sin180) + (40cos270,sin270) = (5, 5?3) + (-10, 10?3) + (-30, 0) + (0, -40) = ( -35, 5?3-40 )) your sketch will confirm that
November 26, 2016

Trigonometry
Both Steve and I both told you what was wrong with the wording of the question. http://www.jiskha.com/display.cgi?id=1480115359 Did you even look at the responses?
November 25, 2016

Math
(2 x 3)>2 - 5>2 is a false statement. you are basically saying: 6 > 2-5 > 2 6 > -3 > 2 the part 6 > -3 is true, but -3 > 2 is nonsense To ask "evaluate" the expression makes no sense Hey, wait a minute! Did you mean (2 x 3)^2 - 5^2 ?? then you...
November 25, 2016

math
You can't just drop the variable. 5(2x + 7) = 10x + 35 Now you can see that we can't add the 10 and 35 since they are "unlike" terms
November 25, 2016

Math
correct
November 25, 2016

math
The 14M, the 3M and the 1M are all expenses so what is 20 - (14+3+1) ?? I get 2 Million
November 25, 2016

Calculus AB
3y^3 + 2x^2 = 5 9y^2 dy/dx + 4x = 0 dy/dx = -4x/9y^2 when y = 1 , 3 + 2x^2 = 5 2x^2 = 2 x = ± 1 , but in quadrant 1, x = 1 dy/dx = -4(1)/9 = -4/9 equation of tangent: y-1 = (-4/9)(x-1) 9y-9 = -4x + 4 4x + 9y = 13 check: http://www.wolframalpha.com/input/?i=plot+3y%5E3+%...
November 25, 2016

Trigonometry
y = cos(3?/4 - x) already is a single function of x, namely the cosine function. I don't understand what else you want to do with it. We know: using cos(A-B) = cosAcosB + sinAsinB cos(3?/4 - x) = cos 3?/4 cosx + sin 3?/4 sin x = -?2/2 cosx + ?2/2sinx = ?2/2 (sinx - cosx...
November 25, 2016

Math
In the original number let the unit place by x then the tens place is 2x, (obviously x < 5) then the number in terms of its value is 10(2x) + x and the number reversed is 10x + 2x the difference between these two is 36, just translate this into Math. 10(2x) + x - (10x + 2x...
November 25, 2016

Math
clearly the 5 has to go in the unit position for the number to be odd At the front, what would be bigger, something 6 hundred or something 8 hundred?
November 25, 2016

Mathematics
let his sales be x .06x + 6000 = 10200 solve for x
November 25, 2016

Maths
330/x - 330/(x+5) = 1/2 That's ok, we end up with a quadratic. Multiply each term by 2x(x+5) 660(x+5) - 660x = x(x+5) 660x + 3300 - 660x = x^2 + 5x x^2 + 5x - 3300 = 0 (x-55)(x+60) = 0 x = 55 or x = -60, we would reject the -60 So your inward speed is 55 km/h, the return ...
November 25, 2016

math
90 = 2x3x3x5 since each pair of equal factors produces a perfect square, we have 3x3, a perfect square. So all we need is another 2 and another 5 How about 2x2x3x3x5x5 = 900 900 = 30^2 , so it is a perfect square, and it is divisible by 90
November 24, 2016

math-factors and multiples
both 40 and 32 divide by 8 both a^3 and a^2 divide by a^2 The GCF is 8a^2
November 24, 2016

math
It is 30a^2
November 24, 2016

math
5 ? m/-3 + 18 add m/3 to both sides 5 + m/3 ? 18 m/3 ? 13 m ? 39 or 5 ? m/-3 + 18 -13 ? m/-3 times -3 39 ? m m ? 39 , same as above
November 24, 2016

math
the slope of the 2nd is -2/16 = -1/8 which is the negative reciprocal of the slope of the first. Thus, the lines are perpendicular.
November 24, 2016

math
I assume we are factoring 25m^6-121m^4 = (5m^3 - 11m^2)(5m^3 + 11m^2)
November 24, 2016

Calculus applications
let the height be 100 cm^3 ?r^2 h = 100 h = 100/(?r^2) S = 2 circles + the sleeve = 2?r^2 + 2?rh = 2?r^2 + 2?r(100/(?r^2)) = 2?r^2 + 200/r you typed it wrong, it should have been 2?r^2 + 200 r^-1 dS/dr = 4?r - 200/r^2 = 0 for a min of S 4?r = 200/r^2 r^3 = 200/(4?) = 25/? r...
November 24, 2016

Math
Now: Marcus ---- x John ------ x+10 5 years from now: John's age = x+15 5 years ago: Marcus = x-5 3(x+15) = x-5 that would give you the silly answer of x = -25 checking now Marcus is -25 John is -15 5 years from now, John is -10 and 5 years ago Marcus was -30 sure enough 3...
November 24, 2016

maths
Without any restrictions, number of committees = C(10,4) = 210 include at least one woman ---> exclude cases of all 4 being men number of ways = 210 - C(5,4) = 205
November 24, 2016

math
now: daughter ---- x years Mary -------- 3x years 4 years ago: daughter : x-4 Mary : 3x-4 (x-4)(3x-4) = 40 3x^2 -16x + 16 = 40 3x^2 - 16x - 24 = 0 I was expecting it to factor, hoping for whole number solution, but .... x = (16 ± ?544)/6 = 6.55 or a negative check: if ...
November 24, 2016

Math
let the two numbers be 9x and 3x then 9x + 3x = 72 .. x = 6 sub into my definition to get the numbers.
November 24, 2016

Math
Find the midpoint of AB, then use your "distance between two points" formula to get CM .
November 24, 2016

Maths
let the numbers be x and x+1 solve: x + x+1 = 39
November 24, 2016

math
your first equation should have been 4x +5 = 37 instead of 4x(5) = 37 but then you miraculously switched it to the right one as you solved it. The answer is correct
November 24, 2016

Further mathematics
x^2 + y^2 = 5xy complet the square: x^2 + 2xy + y^2 = 7xy (x+y)^2 = 7xy take log of both sides 2log(x+y) = log 7 + logx + logy 2log(x+y) - log7 = logx + logy 2log(x+y) - 2log 7^(1/2) = logx + logy 2[ log(x+y) - log ?7] = logx + logy 2 log( (x+y)/?7 ) = logx + logx as required ...
November 23, 2016

algebra~help me
18^(4-4y)=54(?2)^(3y-2) take log of both sides (4-4y)log18 = lof54 + (1/2)(3y-2)log2 4log18 - 4ylog18 = log54 + (3y/2)log2 - log2 4log18 - log54 + log2 = y( (3/2)log2 + 4log18) 3.58972... = (5.4726...) y y = .655941
November 23, 2016

Calculus
so considering t = 0 to correspond with 2016 1000 = A 3^0 , but 3^0 = 1 A = 1000 b) y(5) = 1000 3^(4/3) = .... Use your calculator c) 100000 = 1000 3^(t/4) 1000 = 3^(t/4 take log of both sides log 1000 = log 3^(t/4) 3 = (t/4)log 3 t/4 = 3/log3 t = 12/log3 = appr 25.15 years iv...
November 23, 2016

math
Assuming the farm is a rectangle ... length --- x width = 39 2x + 2(39) = 187.2 find x once you have x, take x/39
November 23, 2016

algebra
How about you showing me some of your steps, now that I have done two very similar to this one for you ?
November 23, 2016

algebra
breath (width) ---- x length -----------x+12 2x + 2(x+12) = 144 carry on
November 23, 2016

algebra
smaller --- x larger --- y Now just translate into Math. 3(y - x) = y+3 3y - 3x = y+3 3x - 2y = -3 ** 3(y+x) = 8x + 2 3y + 3x = 8x + 2 5x - 3y = 2 *** solve ** and *** You should get two whole numbers.
November 23, 2016

Differential calculus
If expanded you would get a standard cubic Its x-intercept are (2,0), (-1,0) and (-3,0) http://www.wolframalpha.com/input/?i=plot+y%3D(x-2)(x%2B1)(x%2B3)
November 23, 2016

maths
let the two numbers be 5x and 7x "it's lam is 210" , I have no clue what that means.
November 23, 2016

maths
I will assume you meant the ninetieth term. If a and d are the first term and common difference respectively, then term(90) = 30 a + 89d = 30 a = 30-89d sum(17) = (17/2)(2a + 16d) = (17/2)(2(30-89d) + 16d) = (17/2)(60 - 162d)
November 23, 2016

Math
Did you make a sketch? 1) sin30° = h/15 h = 15sin30 = 15(1/2) = 7.5 m Very unsafe way to place a ladder, the angle should be > 76° at the ground 2) in reference to the 60° angle, the 13 m is the "adjacent" and you want the "opposite" side ...
November 22, 2016

Statistics
numer of ways = 15 x 14 x 12 = .... (assuming the order matters, and you have specified positions)
November 22, 2016

Math
correct (the jet stream does not just flow over the US )
November 22, 2016

I dont know
they can be any (x,y) such that x^2 + y^2 = 64 e.g. (2 , ?60), (?39 , 5) , (8,0), (8,0), (4?2 , 4?2) etc
November 22, 2016

Algebra2
but log8 2 = 1/3 so log8 (a/2) = log8 a - 1/3
November 22, 2016

math
equilateral ---> all sides are equal, so 3x+2 = 2y-x 4x + 2 = 2y 2x + 1 = y also 3x+2 = y + 3 3x+2 = 2x+1 + 3 x = 2 then y = 5 so each side is 3x+2 = 8 and the perimeter is 24
November 22, 2016

Math
9/(2x) = 15/12 "cross-multiply" 30x = 108 x = 108/30 = 18/5 or 3.6
November 22, 2016

Math
amount of peaches --- x lbs amount of melons ---- y lbs amount of apples ----- 100 - x - y lbs (assume both x and y are whole numbers) 10x + 3.5y + .5(100-x-y) = 100 double every term 20x + 7y + 100 - x - y = 200 19x + 6y = 100 x = (100 - 6y)/19 , clearly 0 < y < 6 by ...
November 22, 2016

10th Grade Math
To have a triangle, the sum of any two sides must be greater than the third side. look at C 5+10< 18 all the others form a triangle
November 22, 2016

maths
The volume of 2 similar objects is proportional to the cube of its linear sides 320/x = 8^3/6^3 512x = 69120 x = 69120/512 = 135 or the side ratio is 6/8 = 3/4 old volume = 8(l)(w) = 320 lw = 40 new volume = 6(3l/4)(3w/4) = 54/16 lw = (54/16)(40) = 135
November 22, 2016

maths
surface area of smaller = 4? r^2 surface area of larger = 4?(3r)^2 = 36?r^2 which is 9 times as great or the area of similar objects is proportional to the square of their linear dimension, so 1^2 : 3^2 = 1 : 9
November 22, 2016

Algerbra
so it will differ only in the constant let the equation be y = -4x + b but (-8,-4) lies on it, so -8 = -4(-8) + b solve for b and write the equation.
November 22, 2016

Trigonometry
tanØ = 4/1 = 4 Ø = 75.96 The angle should be 76° by ratio: 4/1 = 16/x x = 4
November 22, 2016

Math
number of adult tickets sold = 3x number of children tickets sold = 5x 5x = 3x + 180 take over.
November 22, 2016

math
LCD is 5b a/5 +4/b = ab/5b + 20/5b = (ab + 20)/(5b)
November 22, 2016

Algebra
slope of main street = (33-17)/(-22+2) = -4/5 so slope of Grimes Blvd = +5/4 y - 9 = (5/4)(x-80) y = (5/4)x - 100+ 9 y = (5/4)x - 91
November 22, 2016

Math
Follow the same steps I just showed you in your previous problem.
November 22, 2016

Math
number of girls ---- 7x number of boys ---- 5x "there are 8 more girls 10 boys" makes no sense are you saying, "there are 8 more girls than boys" ? which translated into math would be 7x = 5x+8 take it from here
November 22, 2016

maths
done, see below
November 22, 2016

algebra
number of nickels ---- x number of dimes ----- x+10 number of quarters = 37-(x + x+10) = 27 - 2x value of coins = 5x + 10(x+10) + 25(27-2x) = 5x + 10x + 100 + 675 - 50x = 775 - 35 x
November 22, 2016

Math
I don't know, you did not state the rate of interest.
November 22, 2016

maths
volume of wooden rod = ?(2^2)(6) = 24? volume which is submerged = 12? So the volume in the cylinder will change by that amount ?(4^2)h = 12? 16h = 12 h = 12/16 cm = 3/4 cm new depth = 4+3/4 cm = 19/4 cm or 4.75 cm
November 22, 2016

maths
" ... is placed in the tin or floats exactly half 2.what is the New depth of water " Retype in proper English so I can understand it.
November 22, 2016

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