Saturday
February 6, 2016

# Posts by steve

Total # Posts: 37,412

Math
January 20, 2016

Math
surely you can figure out that the answer is 13+13+13+13+13+13 = 13*6 = 78
January 20, 2016

math
just write what they give you: xy = 288 (x-1)(y+1) = xy-3 Now just solve for x and y, and you have 16 by 18. Or, just list the factors of 288 and 285: 9x32, 12x24, 16x18 3x95, 5x57, 15x19 and it's easy to see which pairs work.
January 20, 2016

Math
If she ran x miles on 5 of the days, then we have 5x+12 = 42
January 20, 2016

math
cost is 15x, so 20(x-6) = 15x+480
January 20, 2016

Physical science
2*(10cm)^3 * 11.35g/cm^3 * 1kg/1000g = ? kg
January 20, 2016

Physics
2dm is length, not volume. 2dm^3 = 2(10cm)^3 = 2000cm^3 Now use that to get the mass in g, then convert that to kg.
January 20, 2016

Math
They each started out with x. So, together they had 2x stickers. x+72 = 3(x-72) x+72 = 3x-216 2x = 288
January 20, 2016

science
see https://en.wikipedia.org/wiki/List_of_moments_of_inertia
January 20, 2016

Math
we already went through this. There are 2*2=4 hundredths, so you cannot have 3 times that many ones, since the maximum digit is 9.
January 20, 2016

Mathematics
2x+2y-10 = 150 x+y = 80 area = xy = x(80-x) Just find the vertex of that parabola for maximum area.
January 20, 2016

math
well, 1512 has a number of factors. So, if you pick 21 and 72, then dividing by 2 and adding gives you 46.5 If you pick 84 and 18, then the sum is 51. Maybe you meant the new product, not sum. I'm sure you can figure out what happens then.
January 20, 2016

math
well, the primes are 23 and 29 Now 23+29=52, not both digits are even. Hmmm. Did you mean two-digit even number?
January 20, 2016

Pre-Calc
yeah - so? the expression still evaluates to 1.
January 19, 2016

sinAcosB + cosAsinB = x*x + √(1-x^2)√(1-x^2) = x^2 + 1-x^2 = 1 of course- since if you draw the triangle, you are taking the sine of two angles which add to 90°
January 19, 2016

Pre-Calc
sin(arcsin(x)) = x cos(arcsin(x)) = √(1-x^2) so, if A = arcsinx B = arccosx ain(A+B) = sinAcosB + cosAsinB = x√(1-x^2) + √(1-x^2)*x = 2x√(1-x^2)
January 19, 2016

Math
profit of \$13 per lawn. so, it takes 100 lawns to pay off the \$1300. You are correct.
January 19, 2016

math geometry
Without either a diagram or a description, it's impossible to answer these questions. The parallel lines indicate to me that there are probably some alternate interior/exterior angles adjacent angles alternate angles are equal adjacent angles add to 180 I expect you can ...
January 19, 2016

Math
January 19, 2016

Calculus
for y=e^x, the slope of the normal at x=a is -e^-a for y=lnx, the slope of the normal at x=b is -b. So, we want to find a and b such that the normals through (a,e^a) and (b,lnb) are the same line. That is, y-e^a = -e^-a(x-a) and y-lnb = -b(x-b) eliminating y, we then want -e^-...
January 19, 2016

English
In " Tokyo" Ryo and Tsuruishi have all of the following in common except they both have children they both been married they are familiar with Siberia they are both rebuilding their lives My answer is a
January 19, 2016

Calculus
I think you are missing come values. For linear, figure the constant slope. For exponential, divide two known values to get a power of the growth factor. See your previous post for an example.
January 19, 2016

Calculus - typo?
a^1 = a If you meant f(t) = Qoa^t = Qo(1+r)^t then clearly a = 1+r Qo(1+r)^4 = 72.2 Qo(a+r)^10 = 176.7 Now divide and you have (1+r)^6 = 2.447 Now finding r is easy. After that, you can find Qo.
January 19, 2016

Calculus
Let V = ∫sin^2x dx Since cos^2x is a mirror image of sin^2x, ∫cos^2x dx = V Now, since sin^2x+cos^2x = 1, 2V = ∫[0,π/2] 1 dx = π/2 V = π/4 check: sin^2x = (1-cos2x)/2 ∫sin^2x dx = ∫(1-cos2x)/2 dx = 1/2 (x - 1/2 sin2x) [0,π/2...
January 19, 2016

Math
Awesome thank for the help 😀✌
January 19, 2016

Math
2 years ago my mother was 4 times my age then. In 18 years I will be half my mothers new age. How old am I now? I am so stuck 2 years ago Sx4-M (S+18)=(M+18)/2 Now what do I do
January 19, 2016

please show how to set up this problem
If Jenny gave x dollars, then we have .35*40 + (3/8)*40 + x = 40 14 + 15 + x = 40 x = 11 With word problems, just start writing the facts in symbols. You will end up with equation(s) to solve.
January 19, 2016

math - missing data
you left out the drawing size
January 19, 2016

Calculus
Assuming you mean x = 2e^t cos(t) y = 2e^2 sin(t) you know that x=cos(t) y=sin(t) is a circle, So, this is just a spiral, of radius 2e^t for angle t. http://www.wolframalpha.com/input/?i=x+%3D+2e^t+cos%28t%29%2C+y+%3D+2e^t+sin%28t%29+for+0%3C%3Dt%3C%3Dpi Now, the arc length is...
January 19, 2016

Math
January 19, 2016

fraction maths
in one hour, the taps can fill 1/9 + 1/12 = 7/36 of the tank. So, in 3 hours, they fill 3 times that much: 3*7/36 = 7/12
January 19, 2016

math
if the chords have the same length, they are the same distance from the center. So, x^2 = 4x x = 4 or 0 So, they are 16 units from the center. Or, they are both diameters, passing through the center.
January 19, 2016

Math
sorry - no figures available here. Surely you must have some ideas on this massive homework dump!
January 19, 2016

Math
20 marbles, 1 blue So, P(blue,tails) = 1/20 * 1/2 = 1/40
January 19, 2016

Math
rotate clockwise from the +x axis. Since it's less than a quarter circle, it's in QIV.
January 19, 2016

Algebra
No idea whether the given inequality is correct, but if you're looking for an x which satisfies it, you just have to add 2 everywhere: 5 < x-2 < 11 7 < x < 13
January 19, 2016

geometry
216 = 6^3 = 6^2 * 6, so √216 = 6√6 3√216 = 18√6
January 19, 2016

Math
radius of circle is 2000+6400 = 8400 km. But that does not matter when all we want is the angular velocity. ω = (2πrad)/(3hr) = (2π/3) rad/hr
January 19, 2016

Trig
let's stick with yards. The distance between the goal posts is 6.5 yards. So, since arc length s = rθ, we want θ such that 50θ = 6.5 θ = 0.13 radians = 7.45° But, he can only deviate by 1/2 that, or 3.72° Plug in r=20 for the other part. ...
January 19, 2016

math
Pour milk back and forth so the 3 containers hold the amounts shown: 0 0 10 3 0 7 3 7 0 0 7 3 3 4 3 0 4 6 3 1 6 0 1 9 1 0 9 1 7 2 3 5 2
January 19, 2016

calculus
hmmm. we want the line passing through (a,b) and (c,d) such that c^2 - d^2/3 = 1 b^2 = 8a (b-d)/(a-c) = 4/b (b-d)/(a-c) = 3c/d Due to symmetry, there will be two tangent lines, but one solution is (a,b) = (1/2,2) (c,d) = (-2,-3) See the graphs at http://www.wolframalpha.com/...
January 19, 2016

Maths
Looks like a 5-digit number with two decimal places: abc.de abc.2e abc.24 1bc.24 12c.24 12?.24 There can be a max of 9 ones, but 3*4=12.
January 19, 2016

chemistry
you are reducing the concentration by a factor of 9/21 = 3/7. So, that means you must increase the volume by a factor of 7/3. So, just add 4/3 of the original volume, using the diluting agent. As an example, if you have 3mL of 21% solution, adding 4mL of water will give you ...
January 19, 2016

Math
Thanks for stopping by, bob... If the number of \$25 increases is x, then U = 90-x R = 1300+25x So, that means x = 90-U x = (R-1300)/25 Equate the two expressions and you have 90-U = (R-1300)/25 U = 90-(R-1300)/25 or U = 142 - R/25
January 19, 2016

start writing the facts: p+n+d = 65 n = 2p-4 d = n+13 For elimination, standardize the lines: p+n+d = 65 -2p+n = -4 -n+d = 13 Now visit http://www.gregthatcher.com/Mathematics/GaussJordan.aspx and enter your coefficients, and watch the details emerge.
January 19, 2016

Algebra 2
A handy synthetic division calculator can be found here: http://www.mathportal.org/calculators/polynomials-solvers/synthetic-division-calculator.php You will have to adjust your divisor to account for the leading 3.
January 19, 2016

College Algebra
original dimensions: x and x+5 (x-2)(x+5-2)(1) = 644 Now just solve for x.
January 19, 2016

algebra
200 = .40x Now find x.
January 19, 2016

math
That would be (5/2)*10
January 19, 2016

Math
1500(.0675/12)(4)
January 19, 2016

physics
-519*3.4
January 19, 2016

prepositional calculus
ah. Then does b כ c mean implies? If so, then your initial expression appears correct. Sorry, but I don't know the conductive normal form. Surely google can help with this.
January 18, 2016

propositional calculus
(b ≡ c) mean ( b כ c) ^ (c כ b) But if a,b,c are sets, then (b ≡ c) is either T or F. You cannot then say a כ T So, I guess a,b,c are all T/F values, and using subset notation does not seem correct. Maybe I misunderstand your ≡ operator.
January 18, 2016

(3*12.50 + 20 - 3)*1.06
January 18, 2016

math
actually, given the proper values for sin/cos of x and y, the functions of x+y and x-y will work themselves out correctly.
January 18, 2016

Math
∆y/∆x = 1/2
January 18, 2016

Physics
conserve momentum: 50*10 = (50+100)v
January 18, 2016

Physics
the difference in speeds is 819.017ft/8.5s = 96.355ft/s so, what's wrong with this problem?
January 18, 2016

Algebra
parallel if same slope perp. if slopes multiply to -1.
January 18, 2016

math(epidemiology)
when you're talking about 100 people, expect big numbers if covering a long time.
January 18, 2016

math(epidemiology)
5*20 + 1*10 + 10*70
January 18, 2016

Chemistry 101
volume of lead is 12.52lb * 453.59g/lb * 1cm^3/112.3g = ? cm^3 Add that to the 2500 cm^3 already there. Technically, the final volume of water is still 2500mL, but I think they wanted to know the total volume of contents.
January 18, 2016

math 8
this is called elimination. You try to make one variable disappear, then you can find the other one. Since one equation had 2y and the other had 4y, you multiply one by 2, so you get 4y in both equations. Then when you add 4y and -4y, you get 13x + 0y = 26 and y is gone. Now x...
January 18, 2016

math 8
multiply the top equation by 2 and you have 10x+4y = 22 3x-4y = 4 now add, and the y's go away, leaving 13x = 26 Now you can find x, then y.
January 18, 2016

Calculus
where the denominator is zero.
January 18, 2016

Chemistry 101
mass = volume * density v = pi (6.5cm/2)^2 (100ft * 30.48cm/ft) = 101142 cm^3 you have the formulas and the numbers -- what's the problem?
January 18, 2016

Chemistry 101
250m = 2460ft So, now you can find how many boards it will take. Round up to a whole number of boards. Knowing that, it's then simple to find the cost.
January 18, 2016

Technology
I agree.
January 18, 2016

Algebra 2
we are looking for x, as indicated. of course, to find x, you will need to come up with an equation to solve.
January 18, 2016

Math
If the 2nd and 6th terms are equal, then they must all be the same. Now, if you mean the sum is 4, then we have a+d + a+5d = 4 a+2d = a+10d+24 Now solve for a and d and write the sequence.
January 18, 2016

Math
looks like a Fibonacci sequence, where each term (after the first two) is the sum of the previous two terms. Now just write the next 4 terms.
January 18, 2016

algebra
50.00 + .10*50
January 18, 2016

programming
n and p never change! You need to do something like get_nums(n) { if n==0 return 1;   nums=0   while (n!=0) {     n /= 10;     nums++;   }   return nums; } Since get_nums is call-by-value, the ...
January 18, 2016

Trigonomentry help!!!
still not possible. sinA cannot be greater than 1. 17/3 > 2, so sinA+sinA can never be 17/3, which is almost 6! Better revisit the original problem.
January 18, 2016

math
Since 122+58 = 180, and the 4 angles sum to 360, then if the remaining two angles are equal, the must be 90 and 90, right?
January 18, 2016

Maths
I don't recognize the formula, so I have no idea of the units. But if you know the meaning of each symbol, you can easily look up the units for the quantities involved. As for finding b, it's just normal algebra : multiply by b: bEph = hcT Now divide by Eph: b = hcT/Eph
January 18, 2016

Math
each 3cm cube has faces with area of 9cm^2. So, the base of the block must contain 4 cubes. Naturally, the block, being 6cm tall, has a height of 2 cubes. So, there are 4x2 = 8 cubes. I'll let you come up with an equation which fits those facts.
January 18, 2016

Word problem algebra
If the number below was x, then x + 3x = 2(x+10) x = 10 check: 10+30 = 20+20
January 18, 2016

Trigonomentry help plz!!!
sin3A = 3 sinx cos^2(A) - sin^3(A) = 3sinA(1-sin^2(A)) - sin^3(A) = 3sinA - 4sin^3(A) clearly, x/2 = A x = 2A
January 18, 2016

Calculus, greatest and least values on an interval
certainly they can. In fact, except for the endpoints of the interval, greatest and least values must be stationary points, right?
January 18, 2016

Technology
I like it.
January 18, 2016

MATH
you are correct. A right triangle inscribed in a circle has the diameter as its hypotenuse. I don't know what you mean by "the diameter formula."
January 18, 2016

Physics
after 4.40s, the height is 34.4*4-4.9*4.4^2 = 42.74m At that point, its velocity is (34.4-9.8)*4.4 = 108.24m/s So, now we have the ballistic trajectory of the height 42.7 + 108.24t - 4.9t^2 which has its maximum value at t=11.04 Now just plug that in to find the max height.
January 18, 2016

physics
after 2 seconds, its downward speed is 10*2 = 20 m/s So, you have a velocity with horizontal and vertical components of 10 and 20. Now you can find the speed.
January 17, 2016

Science
no idea. I assume you read the text -- what did it say?
January 17, 2016

maths
(1+r)^3 = 2 2^log_2(5) = 5, so (1+r)^(3*log_2(5)) = 5 3*log_2(5) = 3 * log5/log2 = 6.97 years Makes sense, since 3 years = 2x 6 years = 4x so, 6.97 years = 5x
January 17, 2016

math
since distance = speed * time, 7x + 7(x+18) = 420 2x+18 = 60 x = 21 they were going 21 and 39 mph.
January 17, 2016

algebra
well, just plug it in: (4x+6)/(4x+11) = 8/10 10(4x+6) = 8(4x+11) 40x+60 = 32x+88 8x=28 x = 7/2 I have no idea what side ac is, but its ratio to df is 4/5
January 17, 2016

apostrophes
so, why do you say "quarter's" and not "dime's"? Rule of thumb: MOST plurals do not include an apostrophe!
January 17, 2016

Math
ok ok ok I could have said 1 = 8/8 = 8 * 1/8 1 / (1/8) = 8 that is, if I gave you 1/8 of an apple, how many times would I have to do it to give you a whole apple? 8 times. If that is too hard to visualize, just take a piece of paper Cut it in half. How many pieces? 2. 2 * 1/2...
January 17, 2016

Math
well, how many eighths in a whole? 1 is 8 * 1/8, so 8 * 4/15 = 32/15 Now that's more than a full pool, so it's kind of a stupid question. Where does the extra water go? Once the pool is full, it can't hold any more. 4/15 is about 1/4, so it only takes about 4 hours...
January 17, 2016

AP Physics
hint: constant velocity means zero acceleration. So, the friction force just balances the applied force.
January 17, 2016

Physics
well, you know that the range is R = v^2/g sin2θ So, plug in your values.
January 17, 2016

Chemistry 101
since the cross-section area is pi/4 d^2 = 0.002027 in^2 = 0.0131 cm^2, we have 5lb * 453.6g/lb * 1cm^3/8.92g / .0131cm^2 = 19409cm ≈ 194m
January 17, 2016

Chemistry 101
pi NOT pie!!! You need to look up the densities of Hg and Pb, then multiply each volume by its density to find the two masses. Then just compare them.
January 17, 2016

Mathematics
So, you have s = 0.01 t^4 e^(-.08t) s" = t^2 e^(-.08t)(.000064t^2-.0064t+.12) so, there are inflection points at t = 0, 25, 75 See the graph at http://www.wolframalpha.com/input/?i=+0.01+t^4+e^%28-.08t%29+where+0%3C%3Dt%3C%3D100
January 17, 2016

Calculus
Isn't this just the intermediate value theorem in disguise? f is continuous.
January 17, 2016

maths
length = 38*4 but no distributive property. Now, if the actual space for a car is 4 meters, and there is a boundary of width w between spaces, then length = w + 38(4+w) That uses the distributive property
January 17, 2016

Math
google is your friend. A discussion of this topic is found here https://www.physicsforums.com/threads/sum-of-k-x-k.372124/ and wolframalpha.com says that T = r/(1-r)^2 I'm sure you can find other interesting explorations online.
January 16, 2016

Math Terminology
Terms are separated by + and - signs. In this case, the terms are 3a, 2b, 7. Variables are usually letters or names whose value can be set or calculated. In this case, a and b are the variables. An expressions is any set of terms and operators. In this case, the expressions ...
January 16, 2016