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Question
Evaluate the following:
`int_1^4` f(x) dx where f(x) = `{{:(4x + 3",", 1 ≤ x ≤ 2),(3x + 5",", 2 < x ≤ 4):}`
Sum
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Solution
`int_1^4` f(x) dx = `int_1^2 "f"(x) "d"x + int_2^4 "f"(x) "d"x`
= `int_1^2 (4x + 3) "d"x + int_2^4 (3x + 5) "d"x`
= `[4(x^2/2) + 3x]_1^2 + [3(x^2/2) + 5x]_2^4`
= `[2x^2 +3x]_1^2 + [3/2 x^2 + 5x]_2^4`
= `[2(2)^2 + 3(2)] - [2(1)^2 + 3(1)] + [3/2(4)^2 + 5(4)] - [3/2 (2)^2+ 5(2)]`
= `[2(4) + 6] - [2 + 3] + [3/ (16) + 20] - [3/2 (4) + 10]`
= [8 + 6] – [5] + [24 + 20] – [6 + 10]
= 14 – 5 + 44 – 16
= 58 – 21
= 37
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Definite Integrals
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