Question

8=2000/π/4×(30^2-d2) .find d

Answer 1

SOLUTION :

$\mathtt{8 = \frac{2000}{ \frac{\pi}{40} } \times (30 {}^{2} - d {}^{2}) } \\ \\ \mathtt{8 = 2000 \times \frac{40}{\pi} \times (900 - d {}^{2} )} \\ \\ \mathtt{8 = \frac{80000 \times7}{22} \times (900 - d {}^{2}) } \\ \\ \mathtt{ \frac{8}{900 - d {}^{2} } = \frac{280000}{11} } \\ \\ \mathtt{280000(900 - d {}^{2}) = 88} \\ \\ \mathtt{900 - d {}^{2} = \frac{88}{280000} } \\ \\ \mathtt{900 - \frac{88}{280000} = d {}^{2} } \\ \\ \mathtt{d {}^{2} = \frac{252000000 - 88}{28000} } \\ \\ \mathtt{d {}^{2} = \frac{291999912}{28000} } \\ \\ \mathtt{d {}^{2} = 9000(approx)} \\ \\ \mathtt{d = \sqrt{9000} } \\ \\ \mathtt{d = 30(approx)}$

Answer is d = 30.

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Answer 2

8=40π​2000​×(302−d2)8=2000×π40​×(900−d2)8=2280000×7​×(900−d2)900−d28​=11280000​280000(900−d2)=88900−d2=28000088​900−28000088​=d2d2=28000252000000−88​d2=28000291999912​d2=9000(approx)d=9000​d=30(approx)​ 

Answer is d = 30.