This question is from trigonometry
Topic – trigonometric ratios on complementary angles
We have been asked to prove that (sin72° + cos18°)(sin72° – cos18°)= 0
without using trigonometric tables
RS Aggarwal, Class 10, chapter 12, question no 3(v).
Rajan@2021Guru
Without using trigonometric tables, prove that: (sin72° + Cos18°)(sin72° – cos18°) = 0
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LHS = (sin72° + cos18°)(sin72° − cos18°)
=(sin²72° – cos²18°)
= (sin²72° – cos²(90° – 72°))
= sin²72° – sin²72°
= 0 = RHS