Selangor Trial 2025 Add Maths Paper 1, Question 15Trigonometric Functions

Solved on video in English · Form 5, Trigonometric Functions · 7:28 video

The question

(a)

(Section B) 15 (a) By using trigonometric ratio, find the value of sec 135°.

(b)(i)

(b)(i) Prove that tan x sin 2x = 1 − cos 2x.

(b)(ii)

(b)(ii) Hence, solve the equation 2 tan x sin 2x = 1/4 for 180° ≤ x ≤ 360°.

Step 1

sec 135° = 1/cos 135°.

Why this step

There is no sec button, so we switch to cos using sec = 1/cos, then use the 45° reference angle.

2 more steps, each with the reason for it, in the full solution

Final answer

sec 135° = −√2

Where students lose marks

Watch out: cosine is negative in the second quadrant, so keep the minus sign and simplify to −√2.

5 more steps, each with the reason for it, in the full solution

Final answer

Shown

Where students lose marks

Watch out: use cos 2x = 1 − 2 sin²x, cancel cos x, and show each side clearly ends at 2 sin²x.

6 more steps, each with the reason for it, in the full solution

Final answer

x = 194.48°, 345.52°

Where students lose marks

Watch out: change the range to 360° ≤ 2x ≤ 720° before solving, or you'll miss the correct angles.

Watch every step of this question solved on video (7:28), with the reason behind each step and a box that checks your own answer.

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