# Maths

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I am very greatefull to you if you guide me to solve this problem.

Two circles touch externally. The sum of their areas is 130π cm2 and the distance between their centers is 14 cm. find the radii of the circles?

I tried to solve this problem like this:

Area of the circle = πr2

130πcm2 = 22/7xrxr
130x22/7 =22/7xrxr
22/7xr2 =130x22/7
r2 =130x22x7/7
r2 = 130x22x7/7x22
r2 =130
r =√130
r=√2x5x13.
I tried to do this in the above way. But I couldn't get the answer further.

• Maths -

Call the radii r1 and r2.
The center-to-center distance is
r1 + r2 = 14

The combined area is
130 pi cm^2 = pi(r1^2 + r2^2);
therefore
130 = r1^2 + r2^2

The two equations for r1 and r2 can easily be solved by substitution.

(14 - r2)^2 + r2^2 = 130

196 -28r2 + 2r2^2 = 130
r2^2 -14r2 + 33 = 0
(r2 - 11)(r2 -3) = 0
The radii are 3 and 11 cm

• Maths -

r1+r2=14

r2=14-r1

The sum of circles areas is:

r1^2 * ð + r2^2 * ð = 130ð

ð * ( r1^2 + r2^2 ) = 130ð Divide both sides with ð

( r1^2 + r2^2 ) = 130

r1^2 + ( 14 - r1 )^2 = 130

r1^2 + 14^2 - 2 * r1 *14 + r1^2 = 130

r1^2 + 196 - 28 * r1 + r1^2 = 130

2 * r1^2 - 28 * r1 + 196 - 130 = 0

2 * r1^2 - 28 * r1 + 66 = 0 Divide both sides with 2

r1^2 - 14 * r1 + 33 = 0

This equation have 2 solutions:

r1 = 3

and

r1 = 11

When r1 = 3

r2 = 14 - r1 = 14 - 3 = 11

When r1 = 11

r2 = 14 - r1 = 14 - 11 = 3

3 cm and 11 cm

The sum of circles areas:

3^2 * ð + 11^2 * ð =

9 *ð + 121 * ð = 130ð cm^2

P.S.

If you don't know solve equation:

r1^2 - 14 * r1 + 33 = 0

When you see list of results click on:

When page be open in rectangle type:
r1^2 - 14 * r1 + 33 = 0

and click option solve it!

You will see solution step-by-step.

• Maths -

ð = pi

• Maths -

(14 - r2)^(14 - r2)^2 + r2^2 = 130
what is this ^ symbol represents

• Maths -

madam ......please explain how did u get this step.130 pi cm^2 = pi(r1^2 + r2^2)

• Maths -

how did u get this step.130 pi cm^2 = pi(r1^2 + r2^2)
========================
^ means "to the power"
so

pi r^2 = pie times radius squared
= area of circle of radius r

• Maths -

similar to drwls ......

πr^2 + π(14-r)^2 = 130π
r^2 + 196 - 28r + r^2 = 130
2r^2 - 28r + 66 = 0
r^2 - 14r + 33 = 0
(r-3)(r-11) = 0

r = 3 or r = 11

sub back in my definitions.

• Maths -

Radius of 1 circle = x,radius of2 circle=14-x. Now,area of circle = piR2. So,pi(x2)+pi(14-x)2=130pi. Pi(x2+196-28x+x2)=130pi. Pi at both sides is cancelled So 2x2-28x+196-130=0. 2(x2-14x+33)=0. X2-11x-3x+33=0. X(x-11)-3(x-11)=0. So, x= 3,11

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