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Evaluate the following. ∫(3e)2t+54e2t-5dt

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Question

Evaluate the following.

`int ((3"e")^"2t" + 5)/(4"e"^"2t" - 5)`dt

Sum
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Solution

Let I = `int ((3"e")^"2t" + 5)/(4"e"^"2t" - 5)`dt 

Let `(3"e")^"2t" + 5 = "A"(4"e"^"2t" - 5) + "B" "d"/"dt" (4"e"^"2t" - 5)`

`= 4 "Ae"^"2t" - 5"A" + "B"(8"e"^"2t")`

∴ `(3"e")^"2t" + 5 = (4"A" + 8"B") "e"^"2t" - 5"A"`

Comparing the coefficients of e2t and constant term on both sides, we get

4A + 8B = 3 and - 5A = 5

Solving these equations, we get

A = - 1 and B = `7/8`

∴ I = `int (- 1(4"e"^"2t" - 5) + 7/8 (8"e"^"2t"))/(4"e"^"2t" - 5)` dt

`= - int "dt" + 7/8 int (8"e"^"2t")/(4"e"^"2t" - 5)` dt

∴ I = `- "t" + 7/8 log |4"e"^"2t" - 5|` + c    .....`[int ("f" '("x"))/("f" ("x")) "dx" = log |f ("x")| + "c"]`

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Chapter 5: Integration - EXERCISE 5.3 [Page 123]

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