Saturday

May 28, 2016
Total # Posts: 40,861

**Math**

When a telephone exchange is established, there are 10,000 new phone numbersto use(i.e. 722-0000 to 722-9999). Of these 10,000 phone numbers, how many do not contain the digit "9"? I know I can do it this long way, but how do I do it in a shorter more reliable way. ...
*May 2, 2016*

**Calculus - urgent**

Consider the mass as a bunch of horizontal strips, each with area (x2 - x1) dy and thus mass (x2-x1)y dy = y(√(1+2y/3) - (2y^2-y)) dy Now just integrate from 0 to 1.0989
*May 2, 2016*

**trigonomentry...Very hard**

theta, not tita. let x = 3tanθ x^2 = 9tan^2θ 9+x^2 = 9+9tan^2θ = 9sec^2θ √(9+x^2) = 3secθ so, draw a right triangle. Since tanθ = x/3, those are the two legs, and the hypotenuse is √(9+x^2) Now you can write down sinθ and cosθ
*May 2, 2016*

**Geometry (answer please)**

#1. well, each wire is the hypotenuse of a right triangle, with legs 16 and 10√2 back later for #2.
*May 2, 2016*

**Math**

surely, 3+3+3 feet, no? assuming the ribbon is to go once around the edges of the blanket...
*May 1, 2016*

**Math**

since u.v = |u||v|cosθ we must have cosθ = -1. In other words, v = -u
*May 1, 2016*

**Algebra 1**

B is good.
*May 1, 2016*

**math**

If you're using logs base 10, recall that log(32) = log(10*3.2) = log(10)+log(3.2) = 1+log(3.2) So, just look up log of 3.2 and add 1. Whoa - who uses tables these days?
*May 1, 2016*

**Plane trigonometry**

I don't know what "the five points" are, but here's the graph: http://www.wolframalpha.com/input/?i=2sin%28pi*%28x%2B1%2F2%29%29%2B1
*May 1, 2016*

**trig**

I'll use x for ease of typing tan(x)/(tan(2x)-tan(x)) tan(x)/((2tanx)/(1-tan^2(x))-tan(x)) tan(x)/((tanx(2/(1-tan^2(x)) - 1) 1/(2/(1-tan^2(x)) - 1) (1-tan^2(x))/(2 - (1-tan^2(x)) (1-tan^2(x))/(1+tan^2(x)) (1-tan^2(x))/sec^2(x) (1-tan^2(x))cos^2(x) cos^2(x)-sin^2(x) cos(2x)
*May 1, 2016*

**Algebra**

you are correct.
*May 1, 2016*

**MEASUREMENTS**

15m^2 * (3.28ft/1m)^2 * 1bag/20ft^2 * $2.00/bag = $16.14 you said M^2, then used YD^2. I used meters, but you can fix it. Your units do not work out right, and you lost the 15
*May 1, 2016*

**Exponential Modeling**

on the other hand, given the topic of the posting, 0.10(1+r)^40 = 1.25 (1+r)^40 = 12.5 1+r = 1.065 r = 6.5% per year
*May 1, 2016*

**MATH**

The scores are x x x x x x x x The median is 5, so they are x x x 5 5 x x x or x x x 4 6 x x x or 3 3 3 3 7 7 7 7 In the first case, 5 goals are scored. Otherwise, we need not have any scores of 5.
*May 1, 2016*

**math**

this is discussed at http://mathforum.org/sum95/suzanne/whattess.html google is your friend. Use it.
*May 1, 2016*

**MATH- HELP PLEASE. IM LOST**

the other side is either 3.7Ø or 3.7/Ø
*May 1, 2016*

**Geometry ( helllppp pleaaassse )**

#1. How can working with a single point on the ceiling tell anything about the length of the ceiling? #2. Drop the ladder to the floor, and mark where it hits. The use the ladder to construct a hexagon. Two of the main diagonals intersect at the center of the hexagon, just ...
*May 1, 2016*

**Exponential Modeling**

100 * (1/2)^7
*May 1, 2016*

**Exponential Modeling**

2000 * (1/2)^x
*May 1, 2016*

**Exponential Modeling**

p = 1013 * .88^x check for typos
*May 1, 2016*

**Math**

subtract 32 and multiply by 5/9 C = 5/9 (F-32)
*May 1, 2016*

**Algebra**

try this useful site: http://www.zweigmedia.com/RealWorld/LPGrapher/lpg.html
*May 1, 2016*

**Math**

5/6 * 1/2 = 5/12 you might as well ask, what is 1/2 of 5/6?
*May 1, 2016*

**Math**

a + a+d + a+2d = 24 a+3d + a+4d + a+5d = 51 now simplify the equations and solve for a and d.
*May 1, 2016*

**Geometry**

If the foot of the ladder started out at x ft away from the wall, then we know that the length of the ladder is 2x ft. With a 45° angle, then the two legs are x+8 ft, and the length of the ladder is (x+8)√2. So, now we have 2x = (x+8)√2 x(2-√2) = 8√...
*May 1, 2016*

**Solid Mensuration**

circles can be packed in many ways. If they are in a rectangular lattice then they may be in a 2x3 array, in which case, each circle's diameter is 1 foot. Surely by now you have made some attempt to solve the problem...
*May 1, 2016*

**Matthhh**

the straight-line distance is √(60^2+6^2) = 60.3 ft, so ...
*April 30, 2016*

**Algebra**

since there is a walkway on both sides, each dimension is increased by 2x. A(x) = (20+2x)(15+2x)
*April 30, 2016*

**Algebra**

since time = distance/speed, 6/(90-x) + 6/x = 4.5 x ≈ 1.35 km/hr
*April 30, 2016*

**math**

1 2 3 5 6 6 6 so, it can be 1. or even 1 5 5 5 5 5 6
*April 30, 2016*

**Discrete Mathematics**

26!/(8!12!6!) wow - who'd have thought that the entire set of books would contain only three different titles?
*April 30, 2016*

**CES**

1*22 + 9x = 8(x+22)
*April 30, 2016*

**MATH**

volume = 50*10*20 cm^3 1 liter = 1000 cm^3
*April 30, 2016*

**algebra**

I suspect the subtraction problem is 2x^2+5x-10 3x^2-x+9 ----------------- -x^2+6x-19
*April 30, 2016*

**math**

42 is the answer to the Ultimate Question of Life, the Universe and Everything -- surely it answers your feeble inquiry! Actually, I have no idea what you're talking about. which columns are you talking about? The only thing I can think of is that the line of cars looks ...
*April 30, 2016*

**Math**

well, 1 meter is 100 cm. So, how much is still needed?
*April 30, 2016*

**rio claro west secondar**

0.4^2 * 3.7 = 0.16 * 3.7 = ?
*April 30, 2016*

**math**

bzzt. The new value is 120% of the old one, so it increased by 20%.
*April 30, 2016*

**math**

3 of 8 = 3/8 = .375 = 37.5% t2o killed leaves 6 to share, so adjust the fraction. then subtract to find the change.
*April 30, 2016*

**math**

well, what are the nearby multiples of 500? ... 29,000 29,500 30,000 ... which is closest?
*April 30, 2016*

**maths**

you kidding me? You can't count by twos?
*April 30, 2016*

**Maths**

LCM(30,60,x) = 1500 30 = 2*3*5 60 = 2^2*3*5 1500 = 2^2*3*5^3 x could be 5^3 = 125 or any multiple of 25 consisting only of 2,3,5 as factors GCF(30,60,x) = 10 so, 125 is out, but 250 is in LCM(30,60,250) = 1500 GCF(30,60,250) = 10
*April 30, 2016*

**Math**

what is the difference between 6 and 10? How did you find it? Do the same step with the numbers above recall how to subtract negative numbers: 10 - (-5) = 10+5 = 15
*April 30, 2016*

**Solid Mensuration**

The diameter of the circle is 12 cm. The quadrilateral consists of two congruent triangles, with base 12 and altitude 4. So, its area is 48 cm^2
*April 30, 2016*

**Maths**

what is the difference between 6 and 10? How did you find it? Do the same step with the numbers above recall how to subtract negative numbers: 10 - (-5) = 10+5 = 15
*April 30, 2016*

**GEOMTRY**

1 yard = 3 feet 1 yard = 0.9144 meters 1 foot = 12 inches 1 foot = 0.3048 meters now just do the conversions
*April 30, 2016*

**Calculus**

If the rectangle has height x, then it has vertices (x,0), (x,x), ((20-x)/3,x), ((20-x)/3,0) so, its area is a = x((20-x)/3-x) = 20x/3 - 4x^2/3 da/dx = 20/3 - 8x/3 da/dx=0 at x=5/2, and a(5/2) = 25/3
*April 30, 2016*

**Homework Dump**

No ideas on any of these??
*April 29, 2016*

**Homework Dump**

no ideas on any of these?
*April 29, 2016*

**Algebra**

that is correct.
*April 29, 2016*

**Algebra**

nope. Subtract the exponents. 10^7/10^3 = (10^3 * 10^4)/10^3 = 10^4 or, more brute-force, 10*10*10*10*10*10*10 -------------------------- = 10*10*10*10 10*10*10
*April 29, 2016*

**College Algebra**

4-3(x+1)=2x 4-3x-3 = 2x 4-3 = 5x 1 = 5x x = 1/5 15x^2 + x = 2 15x^2 + x - 2 = 0 x = (-1±√(1+120))/30 = (-1±11)/30 = -12/30,10/30 = -2/5, 1/3 √(4x+5) = x 4x+5 = x^2 x^2-4x-5 = 0 (x-5)(x+1) = 0 x = -1, 5 only x=5 is a solution, since √(-4+5) = &#...
*April 29, 2016*

**Algebra**

6/(√3+2) = 6(√3-2)/-1 = 12-6√3 or, B
*April 29, 2016*

**Algebra**

6/(√3-2) recall that (a-b)(a+b) = a^2-b^2 multiply top and bottom by (√3+2) and you have 6(√3+2) ---------------- (√3-2)(√3+2) = (6√3+12/(3-4) = -6√3-12 check your text for typos. It looks like B except for the extra minus sign.
*April 29, 2016*

**Math/Computer**

try google, something like graphs ms word or something. (3,0) is just a point. Seems like a strange project.
*April 29, 2016*

**Math**

Since you have described no experiment, I will have to rely on the theoretical probability of 1/6, making my answer 50.
*April 29, 2016*

**Algebra**

Nope. What did you do? And use some parentheses: -3/(x+2) - 5/(x+3)
*April 29, 2016*

**math**

list the possibilities: P(WWW) = 2/4 * 1/3 * 0/2 P(BWW) = 2/4 * 2/5 * 1/4 ... P(BBB) = 2/4 * 3/5 * 4/6 then add up all the ones where the 3rd ball is black.
*April 29, 2016*

**@Need Help**

The subscripts are a trick of HTML. Most of the codes do not work on this site, but the sub and /sub tags work. For superscripts, the sup and /sup tags work. enclose the words in <> brackets to make them into HTML tags.
*April 29, 2016*

**@Reiny**

Some of these blokes use log6^(1/36) to mean log6(1/36), which is indeed -2 #2 ln(1/e^4) = ln(e^-4) = -4 #3 ok #4 ok #5 since the other logs specify a base, this must be just a common log, and log 10^8 = 8 #6 log3√3 = log33^(1/2) = 1/2
*April 29, 2016*

**math -.-**

just divide each term in the numerator by the denominator: (x^4+5x^3)/(3x^2) = x^4/(3x^2) + 5x^3/(3x^2) = x^2/3 + 5x/3 or, 1/3 x^2 + 5/3 x
*April 29, 2016*

**Calculus**

πr^2h = 200, so h = 200/πr^2 The cost is thus c = .02*2πrh + .06*2πr^2 = .04πr(200/πr^2) + .12πr^2 = 8/r + .12πr^2 dc/dr = -8/r^2 + .24πr dc/dr=0 when r ≈ 2.2 Now just crank out h and c
*April 29, 2016*

**Math Check**

Surely there should be π somewhere in the answer. And what is the shape of the solid? You have given a semi-circular base, but no other info.
*April 28, 2016*

**Math**

n+d+q = 22 5n+10d+25q = 175 n = 3d now crank it out
*April 28, 2016*

**Math**

just solve for t in -16t^2 + 120t+ 50 = 10 probably the quadratic formula will be helpful.
*April 28, 2016*

**Calculus**

Draw a side view. If the cylinder has radius r, and height h, then r^2+h^2 = 6^2 the volume of the cylinder is thus v = πr^2h = πr^2√(36-r^2) now just find dv/dr=0 and thus the maximum volume's radius.
*April 28, 2016*

**Calculus**

if the squares are of side x, then v = x(12-2x)^2 = 4x^3-48x^2+144x dv/dx = 12x^2 - 96x + 144 = 12(x-2)(x-6) so, v has a max at x=2.
*April 28, 2016*

**Geometry**

if the lateral area is 232pi, then pi rs = 232pi rs = 232 s^2 = r^2+h^2, so s = √(r^2+441) r√(r^2+441) = 232 r = 9.97 So, let's say r=10. Then a = 10√541 = 232.6 If the total area is 232pi, then use the adjusted formula for that.
*April 28, 2016*

**Maths**

the scale is 1cm:5km the area scale is thus 1cm^2:25km^2 multiply that by 405, and you have 405cm^2 : 10125km^2
*April 28, 2016*

**homework**

I assume the axis of rotation is the line y=49. So, the shells have thickness dy, and v = ∫[0,49] 2πrh dy where r = 49-y and h = (7+√(49-y))-(7-√(49-y)) v = ∫[0,49] 2π(49-y)((7+√(49-y))-(7-√(49-y))) dy = 26891.2π you can check...
*April 28, 2016*

**Algebra**

you can't look at the numbers 2,4,6,8,10 and see a common difference? man, you gotta not be trying!
*April 28, 2016*

**Trigonometry**

it is just the graph of csc(x) shifted left by pi/4 see it at http://www.wolframalpha.com/input/?i=csc%28x%2Bpi%2F4%29,+-pi+%3C%3D+x+%3C%3D+2pi
*April 28, 2016*

**Math.**

T4 and T9 are 5 terms apart. So, d=20/5 = 4 T15 = T9 + 6d = 35+6*4 = 59
*April 28, 2016*

**Math**

(x-15)*6 = 48
*April 28, 2016*

**Algebra**

since the denominators are the same, just add numerators. Just as 2/5 + 1/5 = 3/5, -4x/(x+7) - 8/(x+7) = (-4x-8)/(x+7) So, C -2/(x+3) - 4/(x-5) = [-2(x-5) - 4(x+3)]/[(x+3)(x-5) = (-2x+10-4X-12)/[(x+3)(x-5) = (-6x-2)/[(x+3)(x-5) So, A
*April 28, 2016*

**Algebra**

or C,S,U if drawn without serifs, and you don't count the end of a line as an angle.
*April 28, 2016*

**Maths**

1.16x = 1218
*April 28, 2016*

**maths**

86000 * 1.04^4
*April 28, 2016*

**Algebra**

#1 factored, you have (x+3)(x+3)/(x-1) * (x-1)(x-1)/(x-3)(x+3) The (x-1)(x+3) cancels, leaving (x+3)(x-1)/(x-3) so, A #2 The (x-2) cancels, leaving D
*April 28, 2016*

**algebra 1**

you are correct. Although, since formatting is not always clear online, you should say 1/(x-3) so it is not confused with 1/x - 3 which is how 1/x-3 would normally be interpreted.
*April 28, 2016*

**Maths lit grade 11**

#3.1.1: 175*15 + 275*20 + 250*30 = 15625 #3.1.12: each gallon is 3.785 liters, so just multiply #3.1.3: 1 mile = 1609 meters
*April 28, 2016*

**Physics**

2π radians in each circle, so the angular speed is 8π rad/s 2π*0.5 = π meters in each circle, so the linear speed is 4π m/s
*April 28, 2016*

**Math, Pre-Calculus.**

Actually I was wrong earlier, the answer is actually 26 minutes
*April 28, 2016*

**Math, Pre-Calculus.**

No way to tell. All we know is that the distance AC is somewhere between 28 and 154 miles. So, it will take between about 5 and 31 minutes. I suspect you have left something out,
*April 28, 2016*

**Science**

well, the total mass is 540g now do the divisions to get the fractions
*April 28, 2016*

**Algebra**

#1 ok #2 (x+2)/(5x-15) * (10x^2-25x-15) (x+2)/(5(x-3)) * 5(x-3)(2x+1) the 5(x-3) cancels, leaving (x+2)(2x+1) if x≠3
*April 28, 2016*

**College Algebra (pt.3)**

yes, you did it wrong. You left out the t part: 1000 e^.08t = 1750 e^.08t = 1.75 .08t = log(1.75) t = log(1.75)/.08 = 6.99 or, 7 years. surely you didn't think that the money wold almost double in a year and a half at 8%!
*April 28, 2016*

**Algebra**

when dividing, just subtract exponents 4^4/4^6 = 4^(4-6) = 4^-2 = 1/16 or, you could look at it as 4^4/4^6 = 4^4/((4^4)(4^2)) now the 4^4 cancels, leaving 1/4^2 = 1/16
*April 28, 2016*

**College Algebra (pt.2)**

ln(5x-3) = 0 5x-3 = 1 x = 3/5 Your notation is a bit odd. I think you mean log5(x) = 3 x = 5^3 = 125 log2(32) = x 5 = x because 32 = 2^5 log2(3x+1) = 4 3x+1 = 2^4 = 16 x = 5 ^ is usually reserved for exponents, not used in logs.
*April 28, 2016*

**College Algebra**

6^x = 6^(2x-1) x = 2x-1 x = 1 3^x = 1/27 3^x = 3^-3 x = -3 e^(3x) = 10 3x = ln(10) x = ln10/3 = 0.77 50e^(,09t) = 200 e^(.09t) = 4 .09t = ln4 t = ln4/.09 = 15.40 lnx = -0.25 x = e^-.25 = 0.7788
*April 28, 2016*

**Calculus**

lim(√(4+sinx)-2)/(3x) = lim (cosx/(2√(4+sinx)))/3 -> (1/(2√4))/3 = 1/12
*April 28, 2016*

**MATH**

great post!
*April 28, 2016*

**Army school science**

Sorry i was haste in my reply, the answer is actually defined by e=mc^2 unit vector as proven by einstein
*April 28, 2016*

**Army school science**

initial means "at the start" I assume you know what velocity is. So, you are talking about the speed of something at the start of some process.
*April 28, 2016*

**Calculus**

just use the usual distance formula. The distance between (a,b,c) and Ax+By+Cz+D=0 is |Aa+Bb+Cc+D|/√(A^2+B^2+C^2)
*April 28, 2016*

**Algebra**

You can use =/= for not equal. Or, you can find a site with math symbols, and copy/paste the ≠ character. How can you choose both A and C? (x+7) is a common factor, so A is the choice. Similarly, the second one is B. check your math.
*April 28, 2016*

**programming**

cool.
*April 28, 2016*

**Complex Numbers**

you've been posting this over and over. Did you think of google? Many problems posted here have appeared elsewhere. My first hit on google discusses this problem and one similar to it. Scroll down about halfway and you will find what you need. http://math.stackexchange.com...
*April 28, 2016*

**permutations**

there are 3! ways to arrange 3 things.
*April 28, 2016*