# Posts by steve

Total # Posts: 49,762

**Math**

18" = 1.5 ft So, the area of the box is 2(3.5*1.5 + 3.5*2 + 1.5*2) = 30.5 ft^2 Or, using the Ph+2B, we have 2(3.5+1.5)*2 + 2(3.5*1.5) = 30.5 ft^2 Now add the 2.5 to get 33 ft^2 The first formula uses the fact that you have two sets of rectangular faces. The area of each ...

*March 12, 2017*

**Math**

what, you can't plug in t=15?

*March 12, 2017*

**Maths**

The area could also be considered using horizontal strips. In that case, each strip lies between the line and the curve, with no break in the boundary. Then the area is ?[0,27] (y/27 + 2)-?y dy = 27/4

*March 12, 2017*

**Maths**

You cannot just integrate on [0,2] to get the area. That ignores the part between the curve and the line on the interval [2,3]. That is ?[2,3] x^3-(27x-54) dx = 11/4 Add that to your area of 4, and you get 27/4

*March 12, 2017*

**geometry**

Where are P and Q in relation to K and N?

*March 12, 2017*

**Mathematics**

To start with, Construct a right angle. Bisect it. Measure off the lengths. Label the points. Then figure out what the heck angle "DE" is.

*March 12, 2017*

**math**

Suppressing all those trailing zeros, 25b + 10c <= 250 25b >= 50+10c b >= 5 c >= 7

*March 12, 2017*

**Math**

Draw a diagram. It should be clear that if B is h meters tall, (40-h)/10 = tan 26°

*March 12, 2017*

**math**

it is in simplest form if the numerator and denominator have no common factors.

*March 12, 2017*

**Chemistry**

Determine the Enthalpy of combustion of ethyne (C2H2) using the following enthalpies of formation; Data: DHf°(H2O)= -285.9kj/mol DHf°(2H2)= +226.7Kj/mol DHf°(CO2)= -393.5Kj/mol Equation; C2H2--------->CO2 + H2O

*March 12, 2017*

**calculus**

See here: http://www.intmath.com/applications-integration/5-centroid-area.php scroll down for a nice example, with steps for solution.

*March 12, 2017*

**calculus**

the volume of water is 10^2 * ? * 2.5 = 785.4 m^3 That much water weighs 785.4 * 1000 * 9.8 = 7696920 N The center of mass is 1.75m below the top of the pool, so the work required to lift it all is 7696920N * 1.75m = 13,470,000 J But, if you want to use calculus, consider a ...

*March 12, 2017*

**physics**

why do you say it is abnormal?

*March 12, 2017*

**physics**

(70.71i+70.71j)-(0i+100j) = 70.71i-29.29j

*March 12, 2017*

**calculus**

see related problems below.

*March 11, 2017*

**Advanced Functions**

cos(pi/2 - x) = sin(x) so, cos(?/2 - ?/10(t-5)) = sin(?/10(t-5)) you should probably simplify that.

*March 11, 2017*

**Math**

-4 < x < 5 -16 < 4x < 20 -11 < 4x+5 < 25 so, ...

*March 11, 2017*

**Math (Stats)**

I agree

*March 11, 2017*

**Math (Stats)**

So, what does the correlation coefficient tell you about the accuracy of the regression line?

*March 11, 2017*

**geometry**

what, you can't plug in values? A(1) = -2+(1-1)(-2.2) = -2 A(2) = -2+(2-1)(-2.2) and so on hint. Just keep subtracting 2.2 to get the next term.

*March 11, 2017*

**Maths**

To be divisible by 4, the last two digits must be a multiple of 4. Using those digits, the only possibilities are 12,16,28,56,88 There are 5^5 possible 5-digit numbers. Of those, 5^3 * 5 = 5^4 end in those digits. So, 5^4/5^5 = 1/5 of the numbers will be divisible by 4. Adjust...

*March 11, 2017*

**algebra**

z = kyx^2 so, z/(yx^2) = k is constant. So, you want x such that -96/(2x^2) = -84/(7*4)

*March 11, 2017*

**algebra 1**

Take a look here. It's almost the same. http://www.jiskha.com/display.cgi?id=1489212302

*March 11, 2017*

**math**

well, technically, there is no smallest number. You could also multiply any perfect-square fraction with a larger denominator. That will give you an even smaller result. Not an integer, but a fraction as small as you like. just sayin' ...

*March 11, 2017*

**math**

you need all even exponents for a perfect square. 5^3 7^3 3^4 * 5*7 = 5^4 7^4 3^4

*March 11, 2017*

**Math**

geometric, not arithmetic A6 = ar^5 = 9375 A4 = ar^3 = 375 A6/A4 = r^2 = 9375/375 = 25 r = ±5 A9 = A6*r^3 = 9375 * ±125 = ±1171875

*March 11, 2017*

**maths/calculus damon,steve,reiny help steve**

x^3 dy/dx + 3y^2 = xy^2 x^3 dy = y^2(x-3) dx dy/y^2 = (x-3)/x^3 dx -1/y = -1/x + 3/(2x^2) + c 1/y = (3-2x)/(2x^2) + c y = 2x^2/(2x-3+cx^2) y(1) = 1, so 2/(c-1) = 1 c = 3 y = 2x^2/(3x^2+2x-3)

*March 11, 2017*

**Math**

as with any quadratic ax^2+bx+c, the vertex lies on the axis of symmetry, at x = -b/2a In this case, that is x = -1 f(-1) = -1 so the vertex is at (-1,-1) Or, you can complete the square to find the vertex: f(x) = 2x^2+4x+1 = 2(x^2+2x)+1 = 2(x^2+2x+1)+1-2 = 2(x+1)^2 - 1 Recall...

*March 11, 2017*

**math**

or, 3x+7x = 210 10x = 210 x = 21 dogs = 3x = 63 cats = 7x = 147

*March 10, 2017*

**math**

The above answer is clearly wrong, since the total animals is only 210, not just the dogs. d/c = 3/7 7d = 3c d+c = 210 3d+3c = 630 3d+7d = 630 10d = 630 d = 63 so, c=147

*March 10, 2017*

**Math**

f(x) = -(x^2+x-2) = -(x+2)(x-1) The roots are at -2 and +1 So, the vertex and the axis of symmetry are midway between the roots, at x = -1/2 Now just find the y-coordinate of the vertex.

*March 10, 2017*

**Calculus - Derivatives**

x^2 + 5y^3 = 8 2x + 15y^2 y' = 0 y' = -(2x)/(15y^2) y" = - [(2)(15y^2)-(2x)(30yy')]/225y^4 = (60xyy'-30y^2)/(225y^4) = (2xyy'-y^2)/(15y^4) = (2xy'-y)/(15y^3) = 2(2x(-(2x)/(15y^2))-y)/(15y^3) = -2(4x^2+15y^3)/(225y^5)

*March 10, 2017*

**Math**

the right one

*March 10, 2017*

**pre calc**

#1 Po = 1000 Since P(1) = 1.8*P(0), P(t) = 1000*1.8^t To check this, 1000e^(k) = 1800 k = ln(1.8) 1000e^(ln(1.8)*t) = 1000(e^(ln1.8))^t = 1000*1.8^t Or, if you prefer the base e, P(t) = 1000e^(0.5878t) I expect you can handle the rest, now, ok?

*March 10, 2017*

**pre calc**

Surely you can just plug in your numbers. #1: N(4) = 1000*e^.04 #2: 1000*e^.01t = 1700 #3 e^.01t = 2

*March 10, 2017*

**geometry**

Nope. 360/n corresponds to the arc subtended by each side: the central angle. The sum of the interior angles is (n-2)*180 So, (n-2)180/n is the measure of each interior angle of the polygon. Note that 180(n-2)/n = (180n-360)/n = 180 - 360/n This shows that the central angle is...

*March 10, 2017*

**algebra pleeeease help**

#1 triangular pyramid Now, what are your thoughts on the others? Don't expect us to do your whole assignment.

*March 10, 2017*

**Math**

well if 1/3 was left, the whole loaf was 3 times as much. So, how many pieces would that be?

*March 10, 2017*

**math**

1:20000 = 2.7:54000 54000cm = 0.54km

*March 10, 2017*

**Math**

maybe the best choice is the one with the smallest total area -- that is, it uses the least material to make. Or maybe the portion size is such that only one of the containers is a reasonable choice for that amount.

*March 10, 2017*

**Math**

Then I guess you need to start studying, eh?

*March 10, 2017*

**Maths**

you have something against using actual math symbols, as in 12 1/2% lost: 12.5%, leaving 87.5% spent: .70 * .875 = .6125 left: .375 * 1200 = 450

*March 10, 2017*

**need help zigma mathematics**

that's sigma, not zigma. Note that n/(n+1) = 1 - 1/(n+1) So, the sum is the same as n - ? 1/(k+1)! Unfortunately, this cannot be expressed using elementary functions.

*March 10, 2017*

**Math**

then you have not read your material. The base is a square of side 9cm, so its area is 9^2 = 81cm^2 Your formula for volume then tells you it is 1/3 * 81 * 4 = 108 cm^3

*March 10, 2017*

**Math**

v = 1/3 Bh with B=9^2 and h=4

*March 10, 2017*

**math**

5000(1+.09*4)

*March 10, 2017*

**calculus**

1st way: figure the weight of a slice of water in the pool. Integrate that weight through a height of its distance from the top. 2nd way: Figure the weight of all the water in the pool. Its center of mass is 5.5 feet from the top of the pool, so lift that weight 5.5 feet.

*March 9, 2017*

**Math**

18.31 18.29 or, 18.34901326r7812364781263748126478 18.2500000000000000000000036746237642378

*March 9, 2017*

**Math**

month name = input/25 There are, of course, many other possibilities.

*March 9, 2017*

**Math**

well, what is the median of a set of numbers?

*March 9, 2017*

**Algebra**

multiply exponents and you have 16y^-6 / 25x^-8 = 16/25 x^8 y^-6 = 16x^8 / 25y^6

*March 9, 2017*

**Math**

surely you can answer some of this if you draw a diagram. Think about the law of cosines for part 5.

*March 9, 2017*

**Math**

the mean is the average age. The median is the central value. Assuming a similar distribution of ages, a higher mean or median will indicate a higher group of numbers.

*March 9, 2017*

**Math**

looks like the 2nd group were generally older.

*March 9, 2017*

**calculus**

This should clear it up for you... http://math.stackexchange.com/questions/543655/using-hookes-law-to-find-the-work-required-to-stretch-a-spring

*March 9, 2017*

**algebra**

so, did you do it?

*March 9, 2017*

**Hope someone has a Question**

I think you're being irrational. Was there a question in there somewhere, or do I need some transcedental meditation? And if you have hidden some exponents in there somewhere, try using the caret (^) to designate them, as in x^2 means x squared

*March 9, 2017*

**geometry**

Let AD = x The Geometric Mean Theorem states that AD*DB = CD^2 x(20-x) = 25 x = 5(2+?3) Since right triangles ADC and ACB are similar (Angle A is common to both), AC/x = 20/AC AC^2 = 20x = 100(2+?3) AC = 10?(2+?3) = 5(?2+?6)

*March 9, 2017*

**Math**

So, the amounts are in the ratio 5:20 = 1:4 Now it's just like the earlier problem. Use their sum.

*March 9, 2017*

**Math**

oh please. read your earlier post. 8x=80 x=10 so the numbers are 30 and 50, right? That should have been easy just by inspection.

*March 9, 2017*

**Math - Calculus**

I hope it was not you who posted this earlier, where I explained it all. http://www.jiskha.com/display.cgi?id=1489049850

*March 9, 2017*

**Geometry**

Note that each value is multiplied by 3.

*March 9, 2017*

**Math**

well, yes. The next step is to use their sum to actually find x's value: 8x=80 x=10 Now, you can get the two numbers, once you know x.

*March 9, 2017*

**Math**

the numbers are 3x and 5x. so, add them up, solve for x, and ...

*March 9, 2017*

**math**

charity: 5% = 15 saves: 2/5 = 40% = 120 remainder: 175 = 55%

*March 9, 2017*

**pre calc**

It is not (D) because f(x) has a maximum at 35.12 That means that f(x) fails the horizontal line test on the interval (30.24,40), so it is not invertible there.

*March 9, 2017*

**Science**

take just a moment to think about this. Surely you can tell which is the only possible choice. The sun is just a huge, hot ball of gas ...

*March 9, 2017*

**Math**

perpendicular lines have slopes whose product is -1. So, you need -k/6 * -3/2 = -1 k = -4 The 2nd line has slope -3/2. So, its angle of inclination is arctan(-3/2) = -56.3°

*March 9, 2017*

**Math Calculus**

You know what parabolas look like. (x-1)(x-3) is negative between the roots, so this graph has a bump in the middle. Since the axis of symmetry is x=2, f(-1) = f(5) = 8 f(2) = 1 so, the max value is 8 and the minima are 0. f(2) is also a local max, since it is the vertex of ...

*March 9, 2017*

**Math - extreme values**

The critical points are where f' is zero or undefined. It is never undefined. So, remembering your Algebra I, f' = 0 when x=0 or cosx=0: x = odd multiples of ?/2 x=0 is not in the domain, so the only critical points are at x = -?/2 and -3?/2. Naturally, the extreme ...

*March 9, 2017*

**Physics 2017**

measure the diameter of the wire. Then, knowing the weight of the coil, and subtracting the weight of the core, the remaining weight is purely the wire. Now divide the mass of wire by the density to get the volume of wire. Divide that by the cross-section area to get the length.

*March 9, 2017*

**science**

take a look at Snell's Law

*March 8, 2017*

**math**

5C3 if order does not matter

*March 8, 2017*

**Math**

20000*1.05^20 - 15000*1.05^20 = (20000-15000)*1.05^20 = 5000 * 1.05^20 or, consider that the difference is just the amount f interest earned by the extra $5000 that Lisa deposited. 5000*1.05^20 Note that the growth factor is 1.05, not just .05, since .05 gets smaller and ...

*March 8, 2017*

**math**

(x+2)(x-7) <= 0

*March 8, 2017*

**math**

clearly you need roots at -2,1,4 Since p < 0 on the first interval, it must be >0 when x < -2. So, the leading coefficient must be negative, giving us p(x) = -a(x+2)(x-1)(x-4) where a is any positive value. See the graph for a=1 here: http://www.wolframalpha.com/input...

*March 8, 2017*

**Algebra2**

my answer is: x^2/9+y^2/4=1 Sorry about that!

*March 8, 2017*

**Algebra2**

Write an equation of an ellipse in standard form with center at the origin and with the given vertex and co-vertex vertex at (-3,0) and co-vertex at (0.2)

*March 8, 2017*

**Algebra2**

Thank you

*March 8, 2017*

**Algebra2**

I forgot my answer: (x+2)^2 = 4(y-5)

*March 8, 2017*

**Algebra2**

What is an equation of a parabola with the given vertex and focus? vertex(-2,5) focus(-2,6)

*March 8, 2017*

**Probability: Combinations**

6C2 = 6*5/2 = 15

*March 8, 2017*

**Algebra2**

Write an equation of a parabola with a vertex at the origin and a directrix at y=-5. my answer is focus 6,0, directrix =-6

*March 8, 2017*

**Algebra2**

thank you

*March 8, 2017*

**Algebra2**

-3x^2+12y^=84 What are the domain and range My answer domain: all real numbers range: y (less than -) -sqrt7 or sqrt7

*March 8, 2017*

**Algebra2**

What are it's line of symmetry? 4x^2+y^2=9 my answer is it has 2 lines of symmetry, the x and y axis

*March 8, 2017*

**maths**

If there are e erasers, p pencils, and q pens, we have 2e+4p = 240 6e+p+2q = 395 e+p+4q = 415 If A is the matrix of coefficients, then A^-1 = 1/84 (-2 16 -8) (22 -8 4) (-5 -2 22) Then you have (e p q) = (30 45 85) See here: http://www.wolframalpha.com/input/?i=inverse+%7B%7B2,...

*March 8, 2017*

**Science**

No ideas? Surely you have a calculator.

*March 8, 2017*

**Algebra2**

thank you

*March 8, 2017*

**Algebra2**

4x^2+4y^2=64. what are the domain and range? my answer is domain;all real numbers range;-4<=4<=4

*March 8, 2017*

**Math c2**

well, 3?(x^2+1) = ?(9x^2+9) = ?(3x)^2 + 9) So, it looks like a horizontal compression by a factor of 3.

*March 8, 2017*

**Math**

well, for usage over 50 therms, the bill for x therms is y = 67.65 + 1.1917(x-50) So, plug in your y values and solve for the x values.

*March 8, 2017*

**maths**

well, where is x^2-x-6 = 0? You cannot divide by zero, and the square root is not real for negative values, so ... the domain is x values where x^2-x-6 is positive.

*March 8, 2017*

**algebra**

Think about it like this. With 5 types of seeds, there are 5 choices for the 1st flower. For the 2nd flower, there are only 4 choices. For the 3rd flower there are 3 choices. Now you know how many ways the 3 flowers can be planted. But if all you want is the combinations, the ...

*March 8, 2017*

**math**

4x^2+19x-5 = (4x-1)(x+5) The roots (places where the graph crosses the x-axis) are -5 and 1/4 So, where do you think the value is negative?

*March 8, 2017*

**Precaculus**

(0.1 cm^3)/(4?/3 * (5*10^-3 cm)^3) = 0.1/(5.24*10^-7) = 190986 cells V(t) = 0.1 * 2^(t/20)

*March 8, 2017*

**maths**

you know the circumference of a circle is ?d, right? Think of the circle as a round piece of string. Cut it and lay it out straight. That's how far the wheel travels in one complete turn.

*March 8, 2017*

**Math**

sum means add (product means multiply) same mistake. "/" means divide -8n ok your answers are ok if you meant x+(-3) times means multiply. You really seem to have a problem here... and yet you got y-5 correct.

*March 8, 2017*

**Math**

2(80+x) = 410 area = 80x

*March 8, 2017*

**Math**

well, he spent 1/4 + 1/3 + 1/5 = 47/60

*March 8, 2017*