# If sin 3A = 1 and 0 < A < 90°, find tan 2 A − 1 cos 2 A - Mathematics

Sum

If sin 3A = 1 and 0 < A < 90°, find tan^2A - (1)/(cos^2 "A")

#### Solution

sin 3A = 1
sin 3A = sin90°
3A = 90°
A = 30°

tan^2A – (1)/(cos^2"A") = tan^2 30° – (1)/(cos^2 30°)

= (1/sqrt3)^2 – (1)/(sqrt3/2)^2

= (1)/(3) – (4)/(3)

= (–3)/(3)

= – 1

Concept: Trigonometric Equation Problem and Solution
Is there an error in this question or solution?

#### APPEARS IN

Selina Concise Mathematics Class 9 ICSE
Chapter 23 Trigonometrical Ratios of Standard Angles [Including Evaluation of an Expression Involving Trigonometric Ratios]
Exercise 23 (C) | Q 6.3 | Page 298