MathematicsEvaluation of Special Integral FormsJEE Advanced 1978Easy
Visualized Solution (Hindi)
Understanding the Problem
- Given Integral: I=∫sinx−cosxsinxdx
- Our goal is to express the numerator in terms of the denominator and its derivative.
- Denominator (D): sinx−cosx
- Derivative of Denominator (D′): cosx+sinx
The Strategic Manipulation
- Multiply and divide by 2 to manipulate the numerator:
- I=21∫sinx−cosx2sinxdx
Introducing the Denominator and Derivative
- Rewrite 2sinx as (sinx+sinx) and add/subtract cosx:
- 2sinx=(sinx−cosx)+(sinx+cosx)
- Substitute this back into the integral:
- I=21∫sinx−cosx(sinx−cosx)+(sinx+cosx)dx
Splitting the Integral
- Split the fraction into two parts:
- I=21∫(sinx−cosxsinx−cosx+sinx−cosxsinx+cosx)dx
- Simplify the first term:
- I=21∫(1+sinx−cosxsinx+cosx)dx
Integrating the Terms
- Integrate term by term:
- ∫1dx=x
- ∫sinx−cosxsinx+cosxdx=log∣sinx−cosx∣
- Using the property: ∫f(x)f′(x)dx=log∣f(x)∣+C
The Final Answer
- Combine the results:
- I=21[x+log∣sinx−cosx∣]+C
- Final simplified form:
- I=2x+21log∣sinx−cosx∣+C
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