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The radius of a circular disc is increasing at a constant rate of 0.003cm/s. Find the rate at which the area is increasing when the radius is 20cm.

The rate at which the area is increasing, dA/dt, can be written with terms we know or can find out easily: dA/dt=dA/dr x dr/dt.Area of a disc, A = (pi)r^2dA/dr=2(pi)rRate of change of radius, dr/d...

HH
Answered by Henry H. Maths tutor
11790 Views

Factorise 15r+10

Step 1) look at the numbers 

Both 15 and 10 are factors of 5

step 2 ) look at the letters 

there is only one letter 'r' after the 15 

step 3) the...

JL
Answered by Judy L. Maths tutor
9927 Views

How do I solve a simple simultaneous equation?

Simultaneous equations pop up all the time in maths, science, and engineering, so being able to solve them is really useful. Although they can look a bit daunting at first, the same general rules apply...

JM
Answered by Joe M. Maths tutor
4835 Views

Solve the equation log(1-x) - log(x) = 1 where log() is the logarithmic function, base 10.

From the rules of logarithms, we know that:

log(A) - log(B) = log(A/B)

and thus:

log(1-x) - log(x) = log[(1-x)/x]

...

JD
Answered by Joshua D. Maths tutor
22075 Views

A sequence increases by 5 each time and the first term is x. The sum of the first four terms is 54. Set up and solve an equation to work out the value of x.

The first term is x, and if it increases by 5 each time then the second term is x+5, third is x+10, and the fourth is x+15.

Adding these values together we get 4x+5+10+15, and this equals...

TP
Answered by Tom P. Maths tutor
10364 Views

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