Q7 of 46 Page 291

Prove that (sin A + cosec A)2 + (cos A + sec A)2 = 7 + tan2 A + cot2 A

Take left hand side of the given equation:

LHS = (sin A + cosec A)2 + (cos A + sec A)2

Expanding the squares by formula: (a + b)2 = a2 + b2 + 2ab

= sin2 A + cosec2 A + 2 sin A cosec A + cos2 A + sec2 A + 2 cos A sec A 

Rearranging the terms, we get,

= (sin2 A + cos2 A) + 2 sin A cosec A + 2 cos A sec A + cosec2 A + sec2 A

we know that,


=


=


= 5 + 1/(sin2 A cos2 A) …(i)


Now, take right hand side of the equation:


RHS = 7 + tan2 A + cot2 A


=


=


=


=


= 5 + 1/(sin2 A cos2 A) …(ii)


From equation (i) & (ii),


LHS = RHS


Hence, proved.

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