∫ 0 2 x 1 − ( x − 1 ) 2 d x = ?
Give your answer to 2 decimal places.
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You can simplify your second integral by considering the unit circle. Do you see why?
As the Challenge Master notes, the second integral represents the area of a unit semicircle, which has area 2 π .
Came to 2 1 ∫ ( 1 + cos ( 2 θ ) ) d θ and then only solved ∫ cos ( 2 θ ) d θ = 0 f o r g i v e n l i m i t s . and put the answer as 0!! as I often do.
If you put it that way yes answer is pi/2 but if use arcsin(-1) =3pi/2 then the final answer would be -pi/2
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The range of the arcsin function is [ − 2 π , 2 π ] , with arcsin ( − 1 ) = − 2 π , making the final answer 2 1 ( arcsin ( 1 ) − arcsin ( − 1 ) ) = 2 π . Also note that the integrand is non-negative over the interval [ 0 , 2 ] , so the value of the integral cannot be negative.
I know this is an almost unnecessary comment: But for anyone tempted to pick up that calculator on the final step.... no need! Just a reminder: Long division works on pi too..... 3.1415 / 2 = 1.57
my mistake: i thought arcsin − 1 = 3 π / 4 instead of − π / 4
Why odd function equals 0?
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This trick only works when the bounds of the integral are a and − a . The areas on the left hand and right side of such a graph cancel out. Consider sin x for example ... ?
Why don't you first apply some techniques of definite integral and then solve indefinite It would be quite easier
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First let u = x − 1 . Then x = u + 1 , d u = d x and as x : 0 → 2 we have u : − 1 → 1 . The integral then becomes
∫ − 1 1 ( u + 1 ) 1 − u 2 d u = ∫ − 1 1 u 1 − u 2 d u + ∫ − 1 1 1 − u 2 d u .
Now the integrand of the first of these integrals is an odd function, and since we are integrating from − 1 to 1 , this integral evaluates to 0 . Thus we just need to focus on the second of these integrals.
Letting u = sin ( θ ) , we have that d u = cos ( θ ) d θ and 1 − u 2 = cos ( θ ) . The (indefinite) integral then becomes
∫ cos 2 ( θ ) d θ = 2 1 ∫ ( 1 + cos ( 2 θ ) ) d θ =
2 1 ( θ + sin ( θ ) cos ( θ ) ) = 2 1 ( arcsin ( u ) + u 1 − u 2 ) ,
which when evaluated from − 1 to 1 yields 2 1 ( ( arcsin ( 1 ) + 0 ) − ( arcsin ( − 1 ) + 0 ) ) =
arcsin ( 1 ) = 2 π = 1 . 5 7 to 2 decimal places.