Question

area of a circle isguvenby the expression 9πx^2 - 12πx + 4π find the radius of the circle when x = 4 cm​

Answer 1

Answer:

$9\pi(4) {}^{2} - 12 \times \pi \times 4 + 4 \times \pi = \\ 9 \times \pi \times 16 - 48\pi + 4\pi = \\ 144\pi - 48\pi + 4\pi = \\ 96\pi + 4\pi \\ = area \: of \: circle$

but area of circle =

$\pi \times r ^{2}$

$therefore \: \pi \times r {}^{2} = 96\pi + 4\pi \\ = \pi \times r {}^{2} = 100\pi \\ = r {}^{2} = 100 = \\ r = 10$

Step-by-step explanation:

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Answer 2

Answer =10 cm

Step-by-step explanation:Area =9π×4^2-12π×4+4π

= 9π×16-12π×4+4π

=144π-48π+4π

=100π

Area of a circle =πr^2

100π=πr^2

100π÷π=r^2

100=r^2

So,the radius of the circle is 10 cm