Solution
Related Formula
(A + B) = A B + A B (A - B) = A B - A B x = 2 ²((x)/(2)) - 1 = 1 - 2 ²((x)/(2))Core Logic
Given x = (5)/(12) and x in (π, 3π/2) (3rd quadrant), x = (-5)/(13). Find (x/2) and (x/2). Since π < x < (3π)/(2) ⇒ (π)/(2) < (x)/(2) < (3π)/(4) (2nd quadrant, so > 0, < 0).
Step 1: Half Angle Values
x = (-5)/(13) = 2 ²((x)/(2)) - 1 ⇒ 2 ²((x)/(2)) = (8)/(13) ⇒ ((x)/(2)) = - 2√(13) -1 + 2 ²((x)/(2)) = (5)/(13) ⇒ ((x)/(2)) = 3√(13)Step 2: Expression Simplification
The expression is:
E = 7x (13x)/(2) + 7x (13x)/(2) + 7x (13x)/(2) - 7x (13x)/(2)Regrouping:
E = ( 7x (13x)/(2) - 7x (13x)/(2)) + ( 7x (13x)/(2) + 7x (13x)/(2))Using identities (A-B) and (A-B):
E = (7x - (13x)/(2)) + (7x - (13x)/(2)) E = ((x)/(2)) + ((x)/(2))Step 3: Final Calculation
E = 3√(13) + (- 2√(13)) = 1√(13)Pattern Recognition
Expanding and rearranging mixed sine/cosine terms often collapses large coefficients (7x, 13x/2) into their simple difference (x/2).
Chapter Mix
Class 11 Maths: Trigonometric Functions