Monday
February 27, 2017

Posts by Reiny

Total # Posts: 37,807

Algebra
smaller number --- x larger number ---- x+4 3(x+4)/x = 4 + 5/x times x 3(x+4) = 4x + 5 3x + 12 = 4x + 5 7 = x the smaller is 7 , the larger is 11 check: 33/7 = 4 with remainder 5 OK, all is good
January 17, 2017

Pre calc
cos a = 4/5, and a is in quad I Make your sketch and use Pythagoras: x^2 + y^2 = r^2 16 + y^2 = 25 y^2 = 9 y = 3 in quad I so sin a = 3/5 do the same for sin b = -15/17 , b in quad IV x^2 + 225 = 289 x = +8 in quad IV evaluate WHAT expression ? but you now have both sines and ...
January 17, 2017

Pre-Cal
the centre of this one is (0,0) and the major axis lies horizontally, so x^2/a^2 + y^2/b^2 = 1 ** for such an ellipse: a^2 = b^2 + c^2, but c = 4 a^2 = b^2 + 16 sub back into ** x^2/(b^2+16) + y^2/b^2 = 1 but (4,1) lies on it, so 16/(b^2+16) + 1/b^2 = 1 16b^2 + b^2+16 = b^2(b^...
January 17, 2017

Math
from x=7t-2 t = (x+2)/7 from y=-4+3t t = (y+4)/3 (x+2)/7 = (y+4)/3 3x + 6 = 7y + 28 3x - 7y = 22 ---> slope = 3/7
January 17, 2017

math
think of it as y = 0x - 4 and compare it with your famous y = mx + b what do you think?
January 17, 2017

Math
Did you make your sketch? On mine, I have a triangle with sides 100 and 400 and the contained angle of 135° Using the cosine law: x^2 = 100^2 + 400^2 -2(100)(400)cos135° x = 475.992.. To get the angle opposite the side of 400: sinØ/400 = sin135/475.992.. sin&...
January 17, 2017

Calculus algebra review
I think you have a typo and you meant: ((1/(2+h)) -(1/2)) / h if so: = ( (2 - 2 - h)/(2(h+2)) / h = -h/(2(h+2))/h = -1/(2h+4)
January 17, 2017

Math
from the last: 2X+2z= 4 x+z=4 z = 4-x from the first: -X-y-z= -8 z = 8-x-y so 4-x = 8-x-y y = 4 from the 2nd: -4+4y+5z =7 -4 + 16 + 5z = 7 5z = -5 z = -1 then in z = 4-x -1 = 4-x x = 5 x=5, y=4, z=-1
January 17, 2017

Math
3/6 ? why not just say half of the 24 students are boys? So ....
January 17, 2017

math
number bought --- n cost price = 50n selling price = 1.2(50)n = 60n 60n = 600 n = 10
January 17, 2017

Math
Explain what an "over" is.
January 17, 2017

math
amount of pure acid added ---- x litres .1(2) + x = .2(x+2) 2 + 10x = 2(x+2) 2+10x = 2x + 4 8x = 2 x = 1/4 L
January 17, 2017

math
I assume you made the simple sketch and translated the angles of depression given to be the base angles of the two right-angled triangle. Let the distance of the hut with the 60° angle be x, let the other distance be y case1: tan60 = 150/x x = 150/tan60 case 2: ..... y = ...
January 17, 2017

Math
area of smaller = 16 perimeter of smaller = 16 area of larger = 36 perimeter of larger = 24 area of smaller : larger = 16:36 = 4 : 9 perimeter of smaller:larger = 16:24 = 2:3
January 17, 2017

Algebra
width --- x length ---x+9 2x + 2(x+9) = 62 2x + 2x + 18 = 62 4x = 44 x = 11 the width is 11 and the length is 20 check: 2(11) + 2(20) = 62 , as needed
January 17, 2017

math
The question seems too simple. Since there are 16 books, you could pick any of them. So 16 different ways to pick a book. Are you sure that that was all it said?
January 17, 2017

DPS ( Math)
If I understand your question .... 1+2+3+4+...+n = 300 you have an AS with a=1, d=1 sum(n) = (n/2)(2a + (n-1)d) = 300 n(2 + n-1) = 600 n^2 + n - 600 = 0 (n+25)(n-24) = 0 n = 24, since n > 0 term(24) = a + 23d = 1 + 23 = 24
January 17, 2017

math
let the two numbers be 4x and 7x 4x = 36 x = 9 So what is the larger of the numbers ?
January 17, 2017

math
So 2/9 of the full tank remain, (2/9)x = 14 x = 14(9/2) = 63 L
January 17, 2017

AP Calculus
When you say, "I don't understand any of this", I am troubled. This question is as fundamental in beginning Calculus as it gets. Are you taking this course in a traditional classroom setting? What is your background in math that enables you to take Calculus? ...
January 16, 2017

math
open http://davidmlane.com/normal.html enter 70 into SD click on <above> and enter 850 adjust Mean until you get .16 in the area (probability) window I had 780.39 days as the mean.
January 16, 2017

Algebra 2
number of dimes ---- x number of quarters --- x-4 equation based on value: 10x + 25(x-4) = 320 etc
January 16, 2017

Math
How about just using the cosine law? let the distance be x x^2 = 500^2 + 1050^2 - 2(500)(1050)cos 86°
January 16, 2017

Math
Of course you made a diagram. let the distance to the first connection be x let the distance to the second connection by y x < y from the smaller right-angled triangle: sin55 = x/15 x = 15sin55 from the larger triangle: sin 63 = y/22 y = 22sin63 distance between the two ...
January 16, 2017

Algebra 2
correct, it is a) another way would be to look at the regions that each defines and see if the point lies in that region. since you only have two boundaries to worry about, that would be quite easy. So sketch y = 3x -1 , (y-intercept of -1 and slope of 3) and y = -x+1 , (y-...
January 16, 2017

Algebra 2
test your point in each of the cases. I will try c) is 1 > 12-1 and 1 < -4+1 is 1 > 11 and is 1 < -3 I guess not! , so not c) remember , since they use the logical operator "and", both parts must be true
January 16, 2017

Math
6x +12 + 2cosx = 0 or 2cosx = -6x - 12 No straight-forward or easy way to get a reasonably accurate number. Let's start by looking at the graphs of y = 2cosx and y = -6x-12 http://www.wolframalpha.com/input/?i=plot+y+%3D+2cosx+,+y+%3D+-6x-12 looks like there is a solution ...
January 16, 2017

help in "logic" needed - Math
I have seen your post several times. Have not answered it since I am not familiar with the topic. The last time I would have seen something like that must be about 55 years ago and it has long since gone into my "delete" part of my memory.
January 16, 2017

MATH
simply use the "length of line between 2 points" formula. I will do PQ, you do the other two PQ = ?( (7+3)^2 + (3-5)^2 ) = ?(100 + 4) = ?104 = ?4 ?26 = 2?26
January 16, 2017

math
assuming you mean: 225 ÷ 15[60 ÷ 3|10+18 ÷ (9-7)-14|+11] and the | .. | means absolute value = 225 ÷ 15[60 ÷ 3|10+18 ÷ (2)-14|+11] = 225 ÷ 15[60 ÷ 3|10+9-14|+11] = 225 ÷ 15[60 ÷ 3|5|+11] = 15[20|5|+11] = 15...
January 16, 2017

Algebra
y/5+y-3/2=7 I would multiply each term by 10 and see it fall apart and become easy
January 16, 2017

maths
one angle ---- x the other angle ---- 3.5x x + 3.5x = 180° 4.5x = 180 x = 180/4.5 = ... then 3.5x = ...
January 16, 2017

trigonometry
I am sure you made a sketch. On mine, I labeled the window position W, the top of the building across the street T and the bottom of the building B. I also labeled the point where the horizontal from W meets TB as M In triangle WBM, tan20° = 30/WM WM = 30/tan20° in ...
January 16, 2017

Math
4 1/4 + 3 5/8 = 17/4 + 29/8 = 34/8 + 29/8 = ... = ...
January 16, 2017

Geometry
let each side of the square be x then the diagonal is ?2 x by Pythagoras let the short side of the rectangle be a let the longer side be b then (1/2)ab = (.6)(1/2)x^2 ab = .6x^2 10ab = 6x^2 x^2 = (5/3)ab also a^2 + b^2 = 2x^2 , again by Pythagoras, and we are told the ...
January 15, 2017

Geometry
Good link here: https://en.wikipedia.org/wiki/Varignon's_theorem contains a proof which is easy to follow
January 15, 2017

Pre Calc
what is 4(4!/(4-4)! ( 9!/(4!5!) ?
January 15, 2017

Math
Sheena's present age --- x her dad's present age --- 3x in 12 years: Sheena's age = x+12 dad's age = 3x+12 x+12 = (1/2)(3x+12) 2x+24 = 3x + 12 x = 12 Shenna is pesently 12 and her dad is 36
January 15, 2017

Math
let the unit digit be x let the tens digit be y let the hundred digit by (y+1) y+1 + y + x = 20 2y+ x = 19 x = 19-2y, where both x and y must be whole numbers from 0 to 9. the number is 100(y+1) + 10y + x = x + 110y + 100 reverse the hundreds and unit digit: 100x + 10y + y+1...
January 15, 2017

Math
Both are correct In the first one, you don't say how the dot is labeled. Is it a solid dot or an open dot If the dot is solid, it means that value is include and you would have p ? 1 choice C 5x+6<11 5x < 5 x< 1 choice D 5x+6?11 5x ? 5 x ? 1 You decide.
January 13, 2017

math
3/4 on chocolates rest on gum, so 1/4 on gum choc : gum = 3/4 : 1/4 = 3 : 1
January 13, 2017

Math
Don't know what all this is. let the first be x then the second is x+5 and the third = 3(x+5) x + x+5 + 3(x+5) = 75 x+x+5+3x+15 = 75 5x = 55 x = 11 the numbers are 11, 16, and 48
January 13, 2017

Math
Well, 1 teaspoon is half of 2 teaspoons. So what is half of 3.2 cups of sugar ?
January 13, 2017

math
2x dx/dt - 2dy/dt = 0 dy/dt = x (dx/dt)
January 13, 2017

Finance
What did you get so far ?
January 13, 2017

Finance
First find the payment using: Present Value = payment (1 - (1+i)^-n)/i where i is the rate expressed as a decimal , i = .09, and n is the number of interest periods. n = 5 outstanding balance after 2 years = 15000(1.09)^2 - payment( 1.09^2 - 1)/.09 let me know what you get
January 13, 2017

Math - Algebra
Just like it says: 6s +4l = 30 ---as is ---> 6s + 4l = 30 7s + 2l = 23 --times 2--> 14s + 4l = 46 subtract them: 8s = 16 s = 2 in the first ----> 12 + 4l = 30 4l = 18 l = 9/2 or 4.5 the large marble weighs 4.5 g, the smaller 2 g
January 13, 2017

Algebra 2
what is 26x26x10x10x10x10 ?
January 13, 2017

math
The direction of vector AB is (9,8,12) So a plane perpendicular to vector AB will be 9x + 8y + 12z = c, where c is a constant. Let's find the plane such that C(6,2,3) lies on it 9(6) + 8(2) + 12(3) = c c = 106 so the plane containing C and having AB as a normal is 9x + 8y...
January 12, 2017

Calculus
first line derivative: dy/dx = 3(x^2 -4x)^2 (2x-4) = 3(x^2)(x-4)^2 (2)(x-2) = 6x^2 (x-2)(x-4)^2 B is the correct choice, but it is not fully simplified
January 12, 2017

Calculus
k(x)=sin x cos x think: k(x)= (sin x)(cos x) , and use the product rule
January 12, 2017

algebra
The way it was typed and following the order of operation, we have: (v^2 + 6v+8)/(v^2 + v - 12) / (v+2)/(2v-6) = (v+2)(v+4)/( (v+4)(v-3)(v+2)(2)(v-3) ) = 1/(2(v-3)^2) If you meant: (v^2 + 6v+8)/[ (v^2 + v - 12) / ((v+2)/(2v-6)) ] then we would have (v+2)(v+4)/[ (v+4)(v-3)/((v+...
January 12, 2017

Pampers
English ----> Math 4x - 6 = x + 15 solve for x, very easy
January 12, 2017

algebra
I agree if you got -(7c - 25)/p
January 12, 2017

Math
yes!
January 12, 2017

Math
3b + 2m = 7 ---times 2 ---> 6b + 4m = 14 2b + 5m = 6.5 --times 3--> 6b + 15m = 19.5 subtract them: 11m = 5.5 m = .50 sub into first: 3b + 2(.50) = 7 3b = 6 b = 2 Books cost $2 each and magazines cost 50 cents each (wow, good prices, old textbook ??)
January 12, 2017

Calculus
base will be 12 - 2x by 12-2x, height will be x V = x(12-2x)^2 range of x: 0 < x < 6
January 11, 2017

Algebra
5x+3y=9x-7y 10y = 4x y = 2x/5 Not sure what you mean by "solve". Since you have 2 unknowns but only one equation, there is no unique solution. by letting x equal multiples of 5, you will get whole integer solutions for both x and y. e.g. x = 5, y = 2 x = 10, y = 4 x...
January 11, 2017

Calculus
At the max/min of f(x), f ' (x) = 0 , so ?x sinx = 0 ?x=0 ---> x = 0 or sinx = 0 ---> x = 0, ?, 2? We have to find f(x) ? ?x sinx dx ??? ---> nasty tried integration by parts, got messy how about this approach? ?xsinx = ? [?x(x - x^3/3! + x^4/4! - x^5/5! + ...] ...
January 11, 2017

Precalculus
u=4(cos102°i+sin102°j) = 4[cos102° , sin102°] the direction angle is clearly 102° magnitude = ?(16(cos^2 102 + sin^2 102) = ?(16(1)) = 4
January 11, 2017

trigonometry
Make a sketch. I used your A and B as points on the ground, P as the position of the plane and R as a point on the ground directly below P. I let angle A = 50° Enter your given data. angle ABP = 113° Therefore angle APB = 17° by the sine law: PB/sin50 = 3.9/sin17 ...
January 11, 2017

Calculus
your solution and conclusion are correct
January 11, 2017

FAST Angle Help! (Math)
Not enough information. There has be an angle given. What the angle 90°, as I supect? then h^2 = 5^2 + 12^2 = 169 h = 13 (you should remember from now on that the 5-12-13 triangle is right-angled, as well as the most-famous 3-4-5 triangle)
January 11, 2017

math
Just translate ... x = 3y , and y = 3z y+z = 50 3z + z = 50 4z = 50 z = 25/2 or 12.5 then y = 3z = 3(12.5) = 37.5 x = 3y = 3(37.5) = 112.5
January 11, 2017

Math grade 6, quadrilateral logic
False. All parallelograms are trapezoids, but not all trapezoids are parallelograms pictures of trapezoids: https://www.google.ca/search?q=trapezoids&biw=1674&bih=926&tbm=isch&imgil=HGp-jIvhG8bzwM%253A%253B3qIYFYBU0gqV6M%253Bhttps%25253A%25252F%25252Fwww.youtube.com%...
January 10, 2017

value
Interpretation: The simple interest of a certain sum of money for 5 years at 8% is ?200 less than the simple interest on the same sum for 3 years and 4 months at 18%. Find the sum of money. Let the sum of money be x first case: interest = x(.08)(5) = .4x second case: 3 years ...
January 10, 2017

math
In a cyclic quad, opposite angles must add up to 180° let the angles be 2x and 3x so 5x = 180 x = 36 The two angles are 72° and 108°. More information is needed to find the remaining two angles.
January 10, 2017

Math
Who is x and y ? In a rhombus, opposite angles are equal and adjacent angles add up to 180° So the equal angle pairs are 50° and 130°
January 10, 2017

Math
rate = 27 km/hr = 2700000 cm / 60 minutes = 45000 cm/min so in 1 minute, the water flows 45000 cm volume = area of base x height = 5.4 cm^2 x 45000 cm = 243000 cm^3
January 10, 2017

Math
unit cost price = 6/7 or appr .8571 unit selling price = 7/6 or appr 1.1667 profit per unit = 7/6 - 6/7 = 13/42 = appr .3096 or appr 30.96% 13/42 x = 65 x = 65(42/13) = 209.95 or appr 210 210 lemons must be sold
January 10, 2017

9th grade algebra (recursive formula)
or term(18) = 3362 ----> a+17d = 3362 term(38) = 7362 ----> a + 37d = 7362 subtract them: 20d = 4000 d = 200 sub into a+17d = 3362 a = -38 so recursive: term(n) = term(n-1) + 200, term(1) = -38 general: term(n) = a+(n-1)d = -38 + 200(n-1) = 200n - 238
January 10, 2017

Math
You are driving your rental cars only about 1/2 mile and the other at 1/4 mile? I would just walk the distance. Check your typing or the wording of the question.
January 9, 2017

Grade 8 math
I don't know what level of math you are studying at in grade 8 in your region, but you have to know several facts of geometry 1. the Pythagorean Theorem 2. In a right-angled triangle, if a median is drawn from the right angle to the hypotenuse, the length of that median is...
January 9, 2017

Marh
Restate your question in proper English and I will look at it.
January 9, 2017

Math grade 8
not even true, e.g. let x = 1 x^6-x^5-x^4-x^3-x^2-x+1>0 1 - 1 - 1 - 1 - 1 - 1 - 1 + 1 > 0 is false all I needed was ONE exception and the statement is false. see: http://www.wolframalpha.com/input/?i=plot+y+%3D+x%5E6-x%5E5-x%5E4-x%5E3-x%5E2-x%2B1
January 9, 2017

math
2science + 1 auto ----> 5/6w pounds 4science + 2 auto = 2(2science + 1 auto) = 2(5/6w) = 5/3w pounds
January 9, 2017

Math
dR/dq = 30 - .6q so when q = 10 dR/dq = 30 - .6(10) = 24
January 9, 2017

Math
It helps to look at the graph of y = - x^2/(x+3) http://www.wolframalpha.com/input/?i=plot+y+%3D+-(x%5E2)%2F(x%2B3) look at the second graph, the first one is a close-up of the second. The "forbidden" value is x = -3 now look at just a bit to the right of x = -3 What...
January 9, 2017

Math
Sketch your right-angled triangle. sin 32° = 150/x x = 150/sin32 = ....
January 9, 2017

algebra sir reiny sir steve&bob damon help
Confirming Steve's answer, using Wolfram http://www.wolframalpha.com/input/?i=3x%5E2%3Dx%5Ex
January 9, 2017

Math
from : 2p-q-10=0 q =2p-10 sub into the 2nd: (p+10)(q+30) = 7200 (p+10)(2p-10 + 30) = 7200 (p+10)(2p+20) = 7200 divide by 2 (p+10)(p+10) = 3600 p^2 + 20p + 100 = 3600 p^2 + 20p - 3500 = 0 (p-50)(p+70) = 0 p = 50 or p = -70, but p ? 0 p = 50, q = 100-10 = 90
January 9, 2017

algrbra
proper steps: present age of Brandon ---- x present age of Brittney ----- x+5 Three years from now: Brandon------> x+3 Brittney -------> x+5+3 = x+8 x+3 + x+8 = 23 2x = 12 x = 6 Brandon is now 6, and Brittney is 11
January 9, 2017

Math
your choice of A is not correct (2x^5y^2)^3 = 2^3 (x^5)^3 (y^2)^3 = ... review the difference between (x^a)(x^b) and (x^a)^b also what is the meaning of 2^3, it certainly is not (2)(3) like your choice indicates
January 9, 2017

math
why not just solve the equation, they are perfectly set up. subtract them: 6x = -3 x = -1/2 back in #1: -2 + y = 2 y = 4
January 9, 2017

maths
third term of an A.P is 9 ---> a+2d = 9 tenth term is 21 ---> a+9d = 21 subtract them: 7d = 12 d = 12/7 in a+2d=9 a+ 24/7 = 9 a = 39/7 sum(12) = (12/2)( 78/7 + 11(12/7)) = 180
January 9, 2017

maths
I would use substitution. From the 2nd, x = 2y sub into the first: 4(2y) + 2y = 5 solve for y, then find x from x = 2y
January 9, 2017

math
John's present age --- x Uncle's present age ---- 6x in 4 year's time: John will be x+4 Uncle's age will be 6x + 4 6x+4 = 4(x+4) 6x+4 = 4x + 16 2x = 12 x = 6 John is now 6 and the uncle is now 36 in 6 years time the uncle will be 42 uncle's in 6 years time...
January 9, 2017

math
Make a sketch of the 20 by 20 square pool sketch the 2 m wide path all around the square pool Notice that each side is now 24 What is 4 times 24 ?
January 9, 2017

Maths
What is 3x3x2 ?
January 9, 2017

Math
Henry said: 10/35 = 8/W then 10W = 280 W = 28
January 9, 2017

math
so the rate would be 3400/34000 = .1 or 10% so on 38000 the tax would be 3800
January 9, 2017

Math
Damon did this for you on Saturday. What part of his solution did you not like ?? http://www.jiskha.com/display.cgi?id=1483831115
January 8, 2017

Pre-Calculus
radius ---- x height ---- x+5 V = ? r^2 h = ?(x^2)(x+5) , but x = d/2 = ?(d^2/4)(d/2 + 5) = ?( d^3/8 + d^2/4) or = (1/8)?(d^3 + 2d^2) or = (1/8)? d^2(d + 2) or ....
January 8, 2017

Pre-Calculus
make a sketch to see that V = x(11-2x)(8.5 - 2x) = x(93.5 - 39x - 4x^2) = 93.5x - 39x^2 - 4x^3 dV/dx = 93.5 - 78x - 12x^2 = 0 for a max of V solve for x
January 8, 2017

Math- Sequences and Series
n = 1 , S(1) = 1 - 4 = -3 n= 2, S(2) = 4 - 8 = -4 n = 3, S(3) = 9 - 12 = -3 n = 4, S(4) = 16 - 16 = 0 term(1) = -3 term(2) = sum(2) - sum(1) = -4-(-3) = -1 term(3) = sum(3) - sum(2) = -3 -(-4) = 1 term(4) = sum(4) - sum(3) = 0 -(-3) = 3 so the first 4 terms are -3, -1, 1, 3 ...
January 8, 2017

Math
sum(10) = a(r^10 - 1)/(r-1) 699050 = a(4^10 - 1)/3 2097150 = a(1048575) a = 2
January 8, 2017

Math
H(x)= -3x^2+24x-46 = -3(x^2 - 8x + ....) - 46 = -3(x^2 - 8x + 16) - 46 + 48 = -3(x - 4)^2 + 2 vertex is (4, 2) or for f(x) = ax^2 + bx + c the x of the vertex is -b/(2a) for H(x)= -3x^2+24x-46 x of the vertex is -24/-6 = 4 H(4) = -48 + 96 - 46 = 2 vertex is (4,2)
January 8, 2017

Math
What is the method you were taught for this procedure, since there are several ways to do this?
January 8, 2017

Math
a@b = 3a + 2b u@v = 3u + 2v = 20 v@u = 3v + 2u = 20 add them: 5u + 5v = 40 u + v = 8 then 2u@3v = 6u + 6v = 6(u+v) = 6(20) = 120
January 8, 2017

math
Let the number of boys be 3x let the number of girls be 4x ( notice 3x : 4x = 3 : 4 ) given : 4x = 200 x = 50 So we have 150 boys and 200 girls, for a total of 350. ( notice 150:200 = 3:4 , as required)
January 8, 2017

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