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March 23, 2017

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Posts by Reiny

Total # Posts: 38,061

9th grade algebra (completing square)
You seem to have a good grasp of doing these. I verified most of your answers by subbing them back into the original equation. All the ones I tried were correct. I suggest you take your calculator and test your answers.
November 9, 2016

correction - math
Y = 2x^2 + 3?x is NOT a function, since a quadratic must have the form y = ax^2 + bx + c that is, the exponents of the x term can only be 2 or 1 the term ?x is x^(1/2) Furthermore, the graph of a quadratic function is a parabola, the graph of Y = 2x^2 + 3?x looks like this, ...
November 9, 2016

Math
Since no condition is stated, that number would be C(9,5) or 126 There seems to be something missing here.
November 9, 2016

pre calc
amount = a (1/2)^(t/k), where k is the half-life period when t = 2, amount = .7a .7a = a(1/2)(2/k) .7 = (.5)^(2/k) take log of both sides and use log rules log .7 = (2/k)log .5 2/k = log .7 / log .5 = .514573... k = 2/.514573.. = 3.887 days the half-life is 3.89 days check: ...
November 8, 2016

Math HELP HELP
x^2+4x-41 = x^2+4x + 4 - 4 - 41 = (x+2)^2 - 45 expand and simplify to verify my answer
November 8, 2016

pre calc
N = a (2)^(t/20), where N is the number of bacteria, t is the number of minutes, a is the initial count, our problem. counting 7:00 as zero time and 5:00 am as t = 10 hrs = 120 minutes 1000000 = a(2)^(120/20) 1000000 = a(2)^6 64a = 1000000 a = 1000000/64 = 15625 of the germs ...
November 8, 2016

Math
Did you even look at the solution I gave you here http://www.jiskha.com/display.cgi?id=1478637677 This is the same type of problem. btw, the denominator on the right side factors to (x+3)(x-1)
November 8, 2016

Algebra
"j vaires directly with m and inversely with p" ----> j = km/p plug in the given, and solve for k
November 8, 2016

MATH
Your second equation IS a quadratic function. since the highest power you see is x^2. Sorry if you misunderstood. btw, don't say "square root of x", that would be ?x the term is "x squared"
November 8, 2016

MATH
Small change to your definition. The highest power must be a square term. The degree of a polynomial is determined by the highest power, so in your case you would have a cubic because of the x^3 term a quadratic must have the form y = ax^2 + bx + c, where the a,b, and c are ...
November 8, 2016

Math
I will assume you meant: 2x/(x+1) + 3/(5x+5) = 0 the whole thing falls apart when the denominators are zero, since then we would be dividing by zero When does that happen? when x+1 = 0 x = -1 and 5x+5 = 0 5x = -5 x = -1 so x ? -1
November 8, 2016

Math
Look up the definition of a function in your text or in your notes. In a nutshell, it says that for every x there is one and only one y value So, if you see two or more y values for the same x, then it is NOT a function e.g. in the first I see (5,2) and (5,10) , so NOT a ...
November 8, 2016

Calculas-Differentiation
I have now done 2 of your quite straightforward questions. You MUST know how to do these type of relatively easy Calculus problems. Show me the steps of your solution so I can check it.
November 8, 2016

Calculas-Differentiation
The line y=1/4x+1 has a slope of 1/4 So the perpendicular has a slope of -4 y = 6 - x^2 dy/dx = -2x set -2x = -4 , and solve, then use your grade 9 method of finding the equation of the tangent
November 8, 2016

Algebra
amount of the 20% stuff ---- x gallons amount of the other stuff ---- 700-x .2x +.3(700-x) = .24(700) solve for x to reveal the mystery.
November 8, 2016

Calculas-Differentiation
dA/dt = 6t + 1/5 plug in t = 2 for dA/dt
November 8, 2016

trigonometry- hight and distance
At 45° the length of the shadow will also be h m
November 8, 2016

Math
x+y=16 x-y=3 just add them, to find x subtract them to get y
November 8, 2016

Algebra
in its standard form , at centre (0,0) a^2 = b^2 + c^2 4^2 = b^2 + 2^2 b^2 = 12 x^2 / 16 + y^2 / 12 = 1
November 7, 2016

Math
If you are picking just one student, prob(boy) = 12/29
November 7, 2016

Math
why not try it with something like (x+4)(2x-1) expand it and see how many products you have before simplifying
November 7, 2016

Math
to have an undefined slope, the line must be a vertical line. A vertical line has the form x = c, where c is a constant look at our point, its x value is -3 so the equation of your line is x = -3
November 7, 2016

math
radish seeds --- x pumpkins ----- x+6 x + x+6 + 40 = 80 solve for x
November 7, 2016

correction - Math
forget my previous post, did not notice the x^3 f(x)=4x^2-2x+3 ; g(x)=2x^3+4x-7 (f-g)(x) = 4x^2 - 6x + 10 - 2x^3 (f-g)(2) = 16 - 12 + 10 - 16 = -2 bobpursley was correct
November 7, 2016

Math
3rd one: f(x)=4x^2-2x+3 ; g(x)=2x^3+4x-7 (f-g)(x) = 2x^2 - 6x + 10 (f-g)(2) = 8 - 12 + 10 = 6
November 7, 2016

Math
let's take $100 interest earned = 100/9 let the rate be r then the number of years = r 100(r/100)(r) = 100/9 r^2 = 100/9 r = 10/3 = 3 1/3 % for 3 1/3 years in general: amount invested --- x interest earned ---- x/9 rate ----- y/100 time ---- y I = PRT x(y/100)(y) = x/9 y^2...
November 7, 2016

math last question asap ples :P
Well, for A, is 36 + 9 = 64 ?? or , is 6^2 + 3^2 = 8^2 ?? for B, is 144 + 25 = 169 ?? or, is 12^2 + 5^2 = 13^2 ?? btw, just because one of these statements is true, does not "prove" the Pythagorean Theorem, it merely illustrates it.
November 7, 2016

math
difference of squares 16s^2 - 9 = (4s+3)(4s-3)
November 7, 2016

MATH ..can you guys help??? also ASAP :p
simply look what happened to the x and y. It should be clear that (x,y) ----> (x-5, y + 8)
November 7, 2016

stats
prob(right) = 1/4 prob(wrong) = 3/4 prob(at least 15 right) = prob(15 right) + prob(16 right) + ... + prob(40 right) or = 1 - (prob(none right) + prob(1 right) + prob(2 right) + ...+prob(14 right) I hope you have lots of patience and don't make any errors. I will do one of...
November 7, 2016

math
I assume that you mean: "Luis rides his bicycle 3/4 of a mile in 5 minutes" Since 5 minutes is 1/12 of an hour, like you stated rate = distance/time = (3/4) / (1/12) mph = 9 mph
November 7, 2016

pre-calc.
ln(100) = ln(10^2) = 2ln10 so ln100/ln10 = 2ln10/ln10 = 2
November 7, 2016

Pre-Calc
cot x = 1/2 can be written in an infinite number of ways, the 1/2 is simply the ratio expressed in simplest form how about cot x = .5/1 or how about cotx = .378/.756 etc by definition cotx = adjacent side/opposite side in a right-angled triangle so in the original given cotx...
November 7, 2016

Math
x^2 + 2^2 = 5^2 solve for x
November 7, 2016

If y= (2x + 2)^3 find dy/dx using chains rule
I would just do it in one step dy/dx = 2(2x+3)^2 (2) = 4(2x+3)^2 using the steps asked for: let u = 2x+2 du/dx = 2 then y = u^3 dy/du = 3u^2 dy/dx = (dy/du)(du/dx) = (3u^2)(2) = 4u^2 = 4(2x+2)^2 Once you see the pattern of these type of derivatives, you should be able to ...
November 7, 2016

Algebra 2
two consecutive even integers ---> x and x+2 x + x+2 ? 130 2x ? 128 x ? 64 so how about 62 and 64 as the largest pair
November 7, 2016

Math
3 + 6*4 + 3
November 7, 2016

Math
I recognize this to be an circle. Do you want it in standard form? if so, then ... 8x+x^2-2y=64-y^2 x^2 + 8x + ... + y^2 - 2y + ... = 64 complete the square x^2 + 8x + 16 + y^2 - 2y + 1 = 64 + 16 + 1 (x + 4)^2 + (y-1)^2 = 81 centre is (-4,1), radius is 9
November 7, 2016

Calculas
Steve did this for you http://www.jiskha.com/display.cgi?id=1478532807 Why are you reposting?
November 7, 2016

math
the middle term of the expansion is term(10) term(10) = C(20,9)(1)^11 x^9 = 167960x^9 the 9th term is C(20,8) x^8 = 125970x^8 the 12 term is C(20,11) x^11 = 167960x^11 geometric mean = ?(125970(167960)x^19) 167960x^9 = ?(125970(167960)x^19) 167960x^9 = ?(125970(167960))*x^9 ?x...
November 7, 2016

math
Now: Patty ---- x years Sam ----- 4x next year: Patty = x+1 Sam = 4x + 1 4x+1 = 3(x+1) continue
November 7, 2016

math
lw = 24 2l + 2w = 20 l+w = 10 l = 10-w in lw = 24 (10-w)(w) = 24 10w - w^2 = 24 w^2 - 10w + 24 = 0 (w-6)(w-4) = 0 w = 6 , then l = 4 w = 4 , then l = 6
November 7, 2016

Calculas
nothing to see here
November 7, 2016

math
one angle ---- x the other ----- (2/3)x or 2x/3 2(x+2x/3) = 360 2x + 4x/3 = 360 carry on
November 7, 2016

maths
" ... the sum of the first five terms is one-fourth of the next terms." confusing, I will assume you meant: the sum of the first five terms is one-fourth of the next term. i.e. the sum of the first five terms is one-fourth of the 6th terms. a = 2 6th term = a+5d sum(...
November 7, 2016

Math
width ---- x length ---- 3x - 1 2x + 2(3x-1) = 40 carry on
November 7, 2016

math
(5/6)x + 3.60 = 4.35
November 7, 2016

Finance
i = .12 n = 50-18 = 32 amount = 1500( 1.12^32 - 1)/.01 = $457,271.58 where can you get 12% these days?
November 7, 2016

trig help
cosec40(sin40+sin80+cos120) = (1/sin40)(sin40 + sin80 + cos120) = 1 + sin80/sin40 + cos120/sin40 = 1 + 2sin40cos40/sin40 -1/(2sin40) = 1 + 2cos40 - (1/2)csc40
November 7, 2016

algebra
D^2 = 10^2 + 7^2 = 149 D = ?149 = appr 12 , to the nearest whole number
November 7, 2016

maths
width --- x length ---- 3x 2(x+3x) = 1.6 km 8x = 1600 m x = 200 then 3x = 600 The field is 200 m by 600 m for an area of 120,000 m^2
November 7, 2016

@ Joshua - maths
I also have seen this question now for the third time. I also keep ignoring it since it can't be answered with the information given. Include me in the "bad attitude" category.
November 7, 2016

MATH
what is 25000(1 + .0485/4)^24 ?
November 6, 2016

Math
yup, you are right. Need a third cup of coffee. I agree that the question makes no sense.
November 6, 2016

Math
The exterior angles of any polygon add up to 360° so: 3x+2x+4x = 360 x = 40
November 6, 2016

Mathe
I agree with appr 2.83 m but you would round that to 3 m , not 2 m since A and C have no units, I suspect a typo, and one of those was 3 m
November 6, 2016

@ nms, Algrebra readiness
It said " the negative square root of 7" ---> -?7 not " the square root of negative 7" ---> ?-7
November 6, 2016

Algrebra readiness
the negative square root of 7= appr -2.6 so to the nearest integer that would be -3 None of your choices given match that ???? #2 If each square is 2 by 2 ft, its area is 4 ft^2 and 30 of them would give us 120 ft^2 --> we need 170 If each square is 3 by 3 ft, its area is 9...
November 6, 2016

maths
Thanks nms for catching my error I used 2/3 instead of 1/3 (I must have looked back at the wrong fraction)
November 6, 2016

maths
rate of pipe A = 1/15 rate of pipe B = 1/10 combined rate = 1/6 amount done after 4 minutes = 4(1/6) = 2/3 so 1/3 is left to be done time using only A = (2/3) / (1/15) = 10 minutes
November 6, 2016

Math-Trigo
It said "without a calculator" All the work following is done in my head. sinA = -12/13 = y/r x^2 + y^2 = r^2 x^2 + (-12)^2 = 13^2 x^2 + 144 = 169 x^2 = 25 x = ± 5 , but A is in quad IV, so x = 5 so sinA = -12/13, cosA = +5/13 tanA = (-12/13) / (5/13) = -12/5 ...
November 6, 2016

trig
Did you make your sketch? On mine I let Jane's distance to the tower's base be x m, and Bill's distance to the tower be y m There are two right-angled triangles For Jane: tan70° = 34/x x = 34/tan70° do the same step for Bill's distance add x and y
November 6, 2016

Maths
My diagram: A vertical line PQ, to show the tower, P at ground-level Another vertical AB, the points of observation with A at ground-level let AP = x draw a horizontal from B to meet PQ at R in triangle APQ tan 60 = (h+40)/x x = (h+40)/tan60 in triangle BRQ tan30 = h/x x = h/...
November 6, 2016

Calculus
u • v = |u| |v|cosØ, where Ø is the angle between them -4 -21 = ?50 ?25 cosØ -25 = 25?2cosØ cosØ = -1/?2 Ø = 135°
November 5, 2016

Pre-Calculus
(u • v)(u + v) = (-4-21)(<3,4>) = -25<3,4> = <-75, -100>
November 5, 2016

maths
2x=3x subtract 2x from both sides 0 = x
November 5, 2016

Algebra 2
not familiar with your notation does log(30,8) mean log30 8 ?
November 5, 2016

algebra
V = kt/p for the given data: 20 = k(350)/35 k = 20(35)/350 = 2 V = 2t/p when t=330, p=30 V = 2(330)/30 = 22
November 5, 2016

MATH
"y varies inversely with x" ---> y = k(1/x) y = 8 when x = 5 8 = k/5 k = 40 so : y = 40/x plug in x=2, and find y
November 5, 2016

Adv function
I suspect a typo http://www.wolframalpha.com/input/?i=Cos%5E4(x)%2Bsin%5E4(4)%3Dcos(2x) notice the graph of the left side does not intersect the graph of the right side
November 5, 2016

Algebra
a) depends on how you define your variables e.g. let the time be t hours, and the distance be d miles then : d = kt plug in d= 180 and t = 4.5 to solve for k rewrite the equation , now that you know k sub in d = 320 and solve for t
November 5, 2016

Mathe
number of way to have a sum of 4: 13 22 31 number of ways to have a sum of 6: 15 24 33 42 51 prob(sum of 4 OR sum of 6) = 8/36 = 2/9
November 5, 2016

Calculus
Since you are in Calculus, I assume you know the area of a triangle is (1/2) ab sinØ, where Ø is the contained angle between a and b A = (1/2)(4)(4)sinØ A = 8sinØ dA/dØ = 8cosØ for a max of A, 8cosØ = 0 Ø = 90° or 270...
November 5, 2016

Arithmetic
add up the 3 costs, then divide by 3
November 5, 2016

Arithmetic
value of original stock = 75(50) = 3750 after increase of 8%, the value is 3750(1.08) = 4050 number of shares = 4050/50 = 81
November 5, 2016

Math
If I recall, a gross is defined to be 144 so they bought 6(144) or 864 pencils at a weekly use of 24 pencils, the number of weeks = 864/24 or 36
November 5, 2016

math
total profit = 6200-4000 = 2200 number of bikes at $50 profit per bike = 2200/50 = 44
November 5, 2016

math
done later this morning
November 5, 2016

Algebra
7?9 + 5(8-3) = 7(3) + 5(5) = 21 + 25 = 46
November 4, 2016

tri
make a sketch distance along first direction = 5 hrs x 23 knots = 115 n miles distance along 2nd direction = 6(23) = 138 n miles angle between the two directions = 150° by cosine law: x^2 = 115^2 + 138^2 - 2(115)(138)cos 150° = 59756.64... x = 244.45 nautical miles = ...
November 4, 2016

Adv function
"I can't get the l.s to equal r.s" If you are trying to show that it is an identity, good luck , since it is not (try it with 30° for x) So I will assume you are solving: (2-sin^2x)/-sinx=sinx 2 - sin^2 x = -sin^2 x 2 = 0 , which is a contradiction, there is ...
November 4, 2016

math- Trigonometry
I recognize .8641 as an approximation to ?3/2 if cos x = ?3/2 x = 30° sin30° = 1/2 or .5 using your .8641 sinx = .5033
November 4, 2016

algebra 1
or a line parallel to y = 5x - 2 is y = 5x + b , but (8,-2) lies on it -2 = 40 + b b = -42 y = 5x - 42
November 4, 2016

geometry
no idea where A, B, C, D, and O are Cannot be answered as is.
November 4, 2016

Math
selling price = .75(172.36) final price after tax = (1.09)(.75)(172.36) = ...
November 4, 2016

Math
Oh, dear, I think a ban for D&B is certainly due.
November 4, 2016

Tricky Math Question
0^0 is undefined reason: 0^n = 0 for any value of n but a^0 = 1 for any value of a so we have a contradiction, which drives mathematicians crazy, thus it is undefined my 25 year old calculator gives me an error message for 0^0
November 4, 2016

Mathematics
15 > 7 - t/3 The method for solving in-equations is the same as that for solving equation, except: when you multiply or divide by a negative number, you must reverse the inequality sign add t/3 to both sides t/3 + 15 > 7 subtract 15 from both sides t/3 > -8 multiply ...
November 4, 2016

Math
profit = 75 percentage profit = 75/300 = .25 or 25%
November 4, 2016

Math
Repost using proper English.
November 4, 2016

@ anridas - Maths
Please don't post a question as an answer to somebody else's posting. the square numbers less than 144 are 121, 100, 81, 64, 49, 36, 25, 16, 9, 4, 1 ... looks like 16 and 9 are it. since 16 x 9 = 144 or: 144 = 4 x 4 x 3 x 3 = 4^2 x 3^2 = 16(9)
November 4, 2016

Maths
since 1/10 + 2/3 + 1/7 < 1 , there have to be other colours, and yes, it is possible 1/10 + 2/3 + 1/7 = 191/210 minimum counters is 210 191/210 = x/1000 210x = 191000 x = 909.5 but we have to round down since we can't have partial counter, so 909 counters
November 4, 2016

Math
add: 2 1/5 + (1/2)(2 1/5) + (7/8)(2 1/5) = 11/5 + (1/2)(11/5) + (7/8)(11/5) = 11/5 + 11/10 + 77/40 take over, the LCD is 40
November 4, 2016

Algebra
let the certain amount of 8% stuff be x oz .5(8) + .08x = .32(8+x) solve for x
November 4, 2016

mathematics
poorly worded question. We only "solve" equations, you don't have an equation. I will assume you meant: m^2 + 6m + 7 = 0 m^2 + 6m + .... = -7 + ..... m^2 + 6m + 9 = -7 + 9 (m+3)^2 = 2 m+3 = ± ?2 m = -3 ± ?2
November 4, 2016

Maths
so .75x = 8400 x = 8400/.75 = .... "wold" ----> would
November 4, 2016

Math
Bar model??? standard way: Ryan ----- x cans Anne ----- x/2 cans Joel ------ 2x cans x + x/2 + 2x = 1925 (7/2)x = 1925 x = 550 take over
November 4, 2016

Maths.
You don't need a "×" symbol to show multiplication. Use brackets or * or standard algebraic notation e.g. 3×x^2×y ---> 3(x^2)(y) or simply 3x^2 y Furthermore, you will need brackets to eliminate any ambiguity I read yours as: 3x^2 y + (5/8)x^...
November 4, 2016

math
1800 mm = 180 cm = 1.8 m Consider 1 ha as 100 m by 100 m Assume the plough does swaths of 1.8 m up and down. 100/1.8 = 500/9 runs each 100 m long have to be ploughed total distance = (500/9)(100) m time = distance/rate = (500/9)(100) m / 7 km/h = (500/9)(100) m / 7000 m/h = ....
November 4, 2016

Maths
51 = 1+50 = 2 + 49 ... = 50+1 there are 50 such cases out of 50(50) so prob = 50/(50*50) = 1/50 55 , the smallest we can start with is 5 55 = 5 + 50 = 6 + 49 .. = 50 + 5 ----> 46 of them prob = 46/2500 = 23/1250
November 4, 2016

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