Friday

October 9, 2015
Total # Posts: 22,103

**calculus**

d^2y/dx^2 = 6x - 6 dy/dx = 3x^2 - 6 x + c that is zero at x = 2 3*4 -6*2 + c = 0 c = 0 y = x^3 - 3 x^2 + k 1 = 8 - 12 + k k = 5 so y = x^3 - 3 x^2 +5
*August 10, 2015*

**Math**

pi is about 22/7 .25 * pi r^2 =22/(7 *4) = 22/28 = .79
*August 10, 2015*

**Math**

4+7 = 11 so for x 4/11 (0 - -33) + -33 = 12 +-33 = - 21 and for y 4/11(44-0) + 0 = 16 so (-21 , 16)
*August 10, 2015*

**pre-calculus**

same as ratio of circumferences 8 rpm = 8 * 2 pi radians/60 seconds
*August 10, 2015*

**Math**

at 5 seconds it has fallen 16 * 25 at 6 seconds it has fallen 16 * 36 so between 5 and 6 it falls 16(36-25)
*August 10, 2015*

**Algebra II**

1 + (14/7) = 7/7 + 14/7 = 21/7 = 3
*August 10, 2015*

**Math**

There are 13 other hearts there are 3 other aces so there are 16 small winning cards in the deck of 52 16/52
*August 10, 2015*

**calculus**

dy/dx = 3 x^2 so y = x^3 + c -1 = 1^3 + c so c = -2 y = x^3 - 2
*August 10, 2015*

**so**

what is the question?
*August 10, 2015*

**better days**

well g is closer to 9.81 but I will play along. I like to split this in two. It will take two seconds to reach max height at max height, v = 0 but v = Vi - g t so at the top 0 = Vi - 10 t or Vi = 10 (2) = 20 m/s h = Vi t - (g/2) t^2 h = 20 * 2 - 5(4) = 20 meters
*August 9, 2015*

**math**

if a^2 = b/c multiply both sides by c a^2 c = b divide both sides by a^2 c = b/a^2 c^2 = b^2/a^4
*August 9, 2015*

**Calculus - HELP URGENT PLEASE**

y = x^2 x = sqrt y = y^.5 well, you did not give us the choices. There are basically 2 stack round plates r = (2-y^.5) horizontal area of plate = pi r^2 = pi (2 - y^.5)^2 = pi(4 - 4 y^.5 + y) volume = integal y = 0 to y = 4 of pi (4 - 4 y^.5 + y) dy or use vertical cylinders ...
*August 9, 2015*

**math**

Two ways, usually use the second, induction but I like the first: http://mathforum.org/library/drmath/view/56920.html
*August 9, 2015*

**damon or reiny need ur help God bless you**

I guess I will assume the tool is cutting the long way (250 mm) and moving sideways 2 mm each stroke Assuming that, and you can always turn it around and do it the other way, each stroke will be 250 + 5 + 5 = 260 mm long and 2 mm wide. To get 100 mm then we will have to take ...
*August 9, 2015*

**Math**

Nope Write your name on a piece of paper turn that piece of paper 90 degrees clockwise so that someone to your left at the card table can read it. NOW, try those transforms. Which one puts your name in front of you so you can read it?
*August 9, 2015*

**math, unit price**

ah, oh guilt :(
*August 9, 2015*

**math, unit price**

well , perhaps
*August 9, 2015*

**math, unit price**

Now you are really asking the same question over and over with different numbers. You try it.
*August 9, 2015*

**math**

4 is the points per unit defeat, the unit points say it were 376 dollars for 94 fingbats that would be a unit price of 4 dollars per fringbat
*August 9, 2015*

**math**

376/94 = 4 points / enemy defeated
*August 9, 2015*

**Math**

You are welcome :)
*August 9, 2015*

**Math**

LOL, I never thought of not doing the problem but just trying all the answers :) It amounts to the same thing but quicker.
*August 9, 2015*

**Linear programming - got to be kidding**

Surely this is not the same yolanda ? anyway x = tons A y = tons B constraints: x+y >/= 3 20 x + 10 y </= 80 y </= 2x then maximize 300 x + 400 y sketch all the constraints in the first quadrant to find corners above line from (0,3) to (3,0) below line from (0.8 to (4...
*August 9, 2015*

**Math**

SKETCH IT !!!! 3/2 in x and 3/2 in y delta x = 20 3/5 (20) = 12 0 + 12 = 12 3/5 * ( 0-15) in y delta y = -9 15 - 9 = 6 (12,6)
*August 9, 2015*

**physics**

150 million km you mean which is 1.5 * 10^8 km which is 1.5 * 10^11 meters c is about 3 * 10^8 m/s distance = rate * time 1.5 * 10^11 = 3 * 10^8 t (1/2) * 10^3 = 7 so t = about 500 seconds or 8 1/3 minutes
*August 9, 2015*

**Algebra**

a b c = 100 a + 10 b + c a = 2 c reversed c b a = 100 c + 10 b + a 100 a + 10 b + c - 100 c - 10 b - a = 396 99 a - 99 c = 396 but a = 2 c so 198 c - 99 c = 396 99 c = 396 c = 4 then a = 8 so 8 b 4 what if b is 1 ? is 814 - 418 = 396 ???? yes what if b is 3? is 834 - 438 = 396...
*August 9, 2015*

**mechanics**

a+b = 35 a-b = 5 so a = 20 b = 15 c^2 = a^2+b^2 - 2 a b cos C 625 = 400 + 225 - 2 a b cos C so cos C = 0 C = 90 or 270 degrees
*August 9, 2015*

**Pre calc**

1.2 miles * 5280 ft/mile = 6336 ft tan 4 = d/6336 d = 443 feet down 14,000 - 443 =
*August 9, 2015*

**physics**

That is correct and if you were to use the weight for example to calculate a friction force you would do weight = mg, not just m
*August 9, 2015*

**physics**

320,000 m/h /3600s/h = 88.9 m/s v = a t d = (1/2) a t^2 so d= (1/2) v^2/a d = (1/2) (88.9)^2/a but a = 4*165,000 N /33,000 kg = 20.6 m/s^2 (2 g, good grief) so d = (1/2)(88.9)^2/20.6 = 191.6 meters
*August 9, 2015*

**science**

south 10 cos 30 west 10 sin 30
*August 9, 2015*

**physics**

g = about 32 feet/second^2 as I remember from my childhood so (1/2) g = 16 vertical problem Vi = 1670 sin 27 Hi = 500 h = Hi + Vi t - 16 t^2 0 = 500 + (1670 sin 27) t - 16 t^2 solve quadratic for t, use the positive answer, that is time in the air horizontal problem u = 1670 ...
*August 9, 2015*

**Math**

long side - 4 * 2.5 = 10 short side - 2 * 3.5 = 7 so 8
*August 9, 2015*

**Math**

(3/4)(3/4)(6) = 3.375 ft^3/post 3.375 ft^3/post * 1200 posts = 4050 ft^3 but 27 ft^3 = 1 yd^3 4050 ft^3 * 1 yd^3/27ft^3 = 150
*August 9, 2015*

**physics**

weight = normal force = m g = 50.9*9.81 =499 N so .526 * 499 and .311 * 499
*August 9, 2015*

**physics**

say it is y = A sin w t goes up A to sin 90 degrees goes down A to sin 180 degrees goes down another A to sin 270 dgrees goes back up A to sin 360 or zero degrees and starts again up A down 2A up A moved total of 4 A
*August 7, 2015*

**Math**

how about (7/6)1260 = 1470
*August 7, 2015*

**physics**

Well, to make it easy, let's say the tree is 50 meters high. Then the max stone height will be 100 meters. That gives us a vertical problem to solve. What is Vi, initial vertical velocity? (1/2) m Vi^2 = m g h so Vi = sqrt(2 g h = sqrt (200*9.81) = 44.3 m/s so when will it...
*August 7, 2015*

**Physics**

900 (25.9/9.81)
*August 7, 2015*

**physics**

d = 5 * 10^-6 meters area = pi d^2/4 = (pi/4)(25*10^-12) pressure = F/area = 2 / [ (pi/4)(25*10^-12) ] Newtons/meter^2 or Pascals
*August 7, 2015*

**physics**

bullet momentum = m v = .020 v final momentum = (.020 + .400)(20) so v of bullet = (.020 + .400)(20) / (.020) initial Ke = (1/2) (.020) v^2 final Ke = (1/2)(.420)(400) It better be less :) so loss to heat = final Ke - initial Ke
*August 7, 2015*

**Physics**

L = 1 meter Well, there is an easy way and a hard way The easy way is that the potential energy at start is the kinetic energy when it hits PE = m g * height of center of mass = (1/2) m g L when it hits its motion is all rotation about the end on the floor rotational KE = (1/2...
*August 7, 2015*

**Medical Billing**

Part A does hospital Part B does doctor visit I do not know what part C is (medicare advantage programs?) Part D is prescriptions
*August 6, 2015*

**science**

v^2/R radial and 2 tangential a = sqrt( [v^2/R]^2 + 2.8^2 ) but v = 5.4 + 2.8 t
*August 6, 2015*

**Logical Reasoning**

I guess, but Mass Electric only has one line running up my street. If one side goes out, so does the other. Therefore with extreme reluctance I have to agree with D.
*August 6, 2015*

**math**

a + b = 2003 a = 2003 -b b could be 1 and a could be 2002 2 and 2001 3 and 2000 4 and 1999 I think I may get tired of this so . . . 1000 and 1003 1001 and 1002 oops then 1002 and 1001 b is bigger than a, no good so 1001
*August 6, 2015*

**Physics**

5,000 * 3,000 Joules 15 million Joules
*August 6, 2015*

**Calculus**

b is a constant so when 0 = b * (something - b * (something else) b cancels
*August 6, 2015*

**Calculus**

patience, patience, you had it :)
*August 6, 2015*

**Calculus**

T=(a-bcot(theta)/4^4)+(bcsc(theta)/2^4) dT/dtheta =b times -1 (-csc^2)/4^4 +1 (-csc ctn )/2^4 set the derivative to zero for max or min csc^2/2^8 = csc ctn /2^4 csc /ctn = 2^8/2^4 = 16 1/sin / cos/sin = 16 1/cos = 16 cos = 1/16
*August 6, 2015*

**technology**

Copy and paste does notwork here.
*August 6, 2015*

**Math**

well, if the right angle is at B hypotenuse = sqrt(2^2+6^2) = 2 sqrt 10 then perimeter = 8+2 sqrt 10
*August 6, 2015*

**Physics**

North: 100 + 60(.5 sqrt 2 ) = 142 East: 60(.5 sqrt 2) + 120 = 162 Tan angle east of north (compass course made good) = 162/142 = 1.14 so angle east of north = 48.7 degrees distance from start = sqrt(162^2+142^2)
*August 6, 2015*

**math**

c + .1 c = 330,000 c = 330,000/1.1 = 272,727.28
*August 6, 2015*

**math**

Your answer is correct 98,840 is more than the principal, clearly wrong. perhaps they mean in ten years?
*August 6, 2015*

**calculus**

dy = 2 x dx + dx y = x^2 + x + c 7 = 1 + 1 + c so c = 5 and y = x^2 + x + 5 when x = 3 y = 9 + 3 + 5 = 17
*August 6, 2015*

**Math**

7 x > 4000 x > 4000/7 or 571.4 571*7 = 3997 too small 572*7 = 4004, that will do so 572
*August 6, 2015*

**Calculus**

That works too :)
*August 6, 2015*

**Calculus**

watch out for sign errors ! derivative of top = (e^x + e^-x -2) when x = 0 this is 2-2 = 0 derivative of bottom = (1-cos x) when x = 0 this is 1-1 = 0 well that was not a big help so try next derivative top: (e^x - e^-x ) oh my, zero again bottom: sin x also 0 again third time...
*August 6, 2015*

**Math**

80 + 50 = 130 SO C = 50 and we have an isosceles triangle with AB = AC so 2x-12 = x-3 or x = 9
*August 6, 2015*

**what is 5 of 90**

90 + 90 + 90 + 90 + 90 = 450 OR 5*9*10 = 45*10 = 450 WHICH IS ACTUALLY HOW I DID IT BEING A COMMON CORE FAN :)
*August 6, 2015*

**English**

[ I am not sure all private schools require uniforms. ] In contrast to public schools which are free to the families of students private schools require tuition as a rule. Moreover private schools can limit their student body to good students or good football players whereas ...
*August 6, 2015*

**pre algebra final exam**

1/3 to 0 is - 1/3 0 to 1 is one so it is not an arithmetic sequence which is constant difference 1/3 * 0 = 0 0 * nothing I know of = 1 so it is not a geometric sequence now let's see if we can find some other pattern 1/3 to 0 = - 1/3 0 to 1 = +1 1 to - 2 = -3 maybe ...
*August 6, 2015*

**DPS sub: science ( chemistry)**

Glad you came along DrBob !
*August 6, 2015*

**DPS sub: science ( chemistry)**

sodium + H2O is a bit violent I would bet on S because H2S is not only stinky but acid
*August 6, 2015*

**So ?**

What ?
*August 6, 2015*

**maths**

the number is a b or b a b = 7 and a = 2 so 7 2 or 2 7
*August 6, 2015*

**maths**

a + b = 9 ------------------ b a - a b = 45 10 b + a - 10 a - b = 45 9 b - 9 a = 45 b - a = 5 ----------------------- so +a + b = 9 -a + b = 5 ____________ add 2 b = 14 b = 7 then a = 2 so maybe 27 or 72? well he overcharged by 45 so I suppose it should have been 27 and he ...
*August 6, 2015*

**Math**

7.5 * 12
*August 6, 2015*

**maths**

integral x^x dx ? Well, really there is no easy way. Here is some reading on it: http://math.stackexchange.com/questions/141347/finding-int-xxdx
*August 6, 2015*

**Calculus**

one way: when t = 0 x = 3 y = 5 dy/dx = dy/dt * dt/dx dy/dt = -5 e^-t dx/dt = 3 e^t so dt/dx = (1/3) e^-t dy/dx = -5 e-t (1/3)e^-t dy/dx = -(5/3) e^-2t = -5/3 when t = 0 so y = -5/3 x + b 5 = -5/3 * 3 + b b = 10 so y = -5 x/3 + 10
*August 5, 2015*

**Chemistry**

It is possible she got this a a unit conversion problem in chemistry. The way I did it is a chemistry and physics way. mols/lter * molecules/mol etc
*August 5, 2015*

**Chemistry**

if the top is the same as the bottom, you are really multiplying by one, just in different languages :)
*August 5, 2015*

**Chemistry**

50,000 ft (1 mile/5280 ft) ft cancels and you have 50,000/5280 miles to do unit conversions multiply so the units cancel feet ( 1 miles/5280 feet) --- > miles or the other way miles (5280 feet/mile) ----> feet
*August 5, 2015*

**Statistics**

get 8 , 9 or 10 right p right = .2 p not right = .8 binomial distribution p 8 out of 10 = C(10,8)* .2^8 *.8^2 = 45 * 2.56*10^-6 * .64 = 73.7*10^-6 p 9 out of 10 = C(10,9)*.2^9 * .8^1 = 10 * 5.12*10^-7 * .8 = 4.096*10^-6 p 10 out of 10 = 1*.2^10 = .1024*10^-6 add 78 * 10^-6 78 ...
*August 5, 2015*

**Chemistry**

8 minutes = 8 * 60 seconds = 480 seconds 186,000 mi/s * 480 s =
*August 5, 2015*

**physics**

.979 * 8.73 = 8.55 meters along the path .32 theta = 8.55 so theta = 26.7 rad yes
*August 5, 2015*

**Math**

3600 seconds/hr * 2 hr = x *60*24 yes
*August 5, 2015*

**algebra/ math**

n = (2^6) (64)^t if t = 1/2 n = (2^6) (64)^.5 but the square root of 64 is 8 so n = 2^6 * 8 which is 2^6 * 2^3 which is 2^9 which is 512 by the way 2^6 = 64
*August 5, 2015*

**Math**

I see 6 :)
*August 5, 2015*

**Math**

(75 * 30 * 6 )ft^3 * 7.5 gal/ft^3
*August 5, 2015*

**mathematics**

another typo when t = 0 , v = 67,000 + 9,000 * 0 when t = 1 , V = 67,000 + 9,000 * 1 when t = 2 , V = 67,000 + 9,000 * 2 etc
*August 5, 2015*

**mathematics**

I have a typo, forgot thousands V(t) = 67,000 + 9,000 t It asked you to write V(t) as a function of t where t is the years since you bought the house. when t = 0 , V = 67,000 + 9,000 * 1 when t = 2 , V = 67,000 + 9,000 * 2 etc
*August 5, 2015*

**mathematics**

if linear (doubt that really by the way) V(t) = 67,000 + (130,000-67,000) t/7 = 67,000 + 9 t
*August 5, 2015*

**math**

factor it ---> (x-1)(x+4) not (x-4) 1 is a factor of anything
*August 5, 2015*

**alg1**

divide by 4 first 2 m^2 + 5 m - 3 = 0 (2m-1)(m+3) = 0 m = 1/2 or -3
*August 5, 2015*

**Math**

say 179 degrees supplement = 1 degree complement of supplement = 89 degrees say 91 degrees supplement = 89 degrees complement of supplement = 1 degree so between 0 and 90
*August 5, 2015*

**Mathematics**

Actually it could be tricky if studying compound interest. .14 times whatever the house is worth now value = 70,600 (1.14)^n amount earned in year n = 70,600[ (1.14)^n - (1.14)^(n-1)]
*August 5, 2015*

**physics**

If the elevator is not accelerating it is not part of the problem. I bet you can do it ignoring the elevator. By the way the mass of the block is also irrelevant because it cancels (remember feathers and rocks fall together in a vacuum)
*August 5, 2015*

**typo I think**

x^2x+6 ????
*August 5, 2015*

**math**

50 words/min * 30 min = 30*50 words 1500
*August 5, 2015*

**Precalculus (Logarithmic)**

oh, well if e^x - 4 = 1/2 then e^x = 4.5 x = ln 4.5 but I wonder if that is what you mean your book does not need parentheses as it does not need ^ sign for expoinents. However on computer keyboard you must be more careful.
*August 5, 2015*

**Precalculus (Logarithmic)**

ln e^(2x) = 2x = ln (15) next two lack parentheses so I do not know if you mean e^(x-4) or e^x - 4 If you just left the parens out, the bunch are right
*August 5, 2015*

**Math**

specific heat * .55 * (100-57)
*August 5, 2015*

**Physics**

m a = m d^2x/dt^2 = -k x .66 d^2x/dt^2 = -23.7 x let x = A sin (wt-phi) where w = 2 pi f then v = dx/dt= A w cos(wt-phi) and a = d^2x/dt^2 = -Aw^2 sin (wt-phi) = - w^2 x so -m w^2 x = - k x snd w^2 = k/m w = sqrt(k/m) = sqrt(23.76/.66) = 6 radians/s so in the end x = A sin (6 ...
*August 5, 2015*

**Physics**

when t = 0, argument of cos = pi when does it equal pi + 2 pi? when 6 pi t = 2 pi or T = (1/3) second or f = 1/T = 3 Hz amplitude is 2 of course phase = -pi or however your book defines phase 2 cos (6*pi*.27 + pi) 2 cos (8.23 radians) 2 cos (471.6 degrees) because I am too ...
*August 5, 2015*

**physics**

Horizontal problem: u = 400 cos 30 forever range = u t where t is the time from the vertical problem Vertical problem: Hi = 300 meters Vi = 400 sin 30 = 200 m/s v = Vi - 9.81 t h = Hi + Vi t - 4.9 t^2 0 = 300 + 200 t - 4.9 t^2 solve that quadratic for t (the positive root, not...
*August 3, 2015*

**Math**

original amount = x spent 1/3 of x so left with 2 x/3 lost half of that so left with x/3 so x/3 = 10 x = 30 dollars
*August 3, 2015*

**Geometry**

average x and average y x = (-4+8)/2 = 2 y = (8-4)/2 = 2 so (2,2)
*August 3, 2015*