Q1
What is sin 30°?
A1/2
B1
C0
D√3/2
ICSEClass 9 (ICSE)MathematicsCh 23 · Topic 1
Trigonometrical Ratios of Standard Angles
Standard angles like 0°, 30°, 45°, 60°, and 90° have specific, memorable trigonometric ratio values used frequently in problem-solving.
Core concept
sin 0°=0, sin 30°=1/2, sin 45°=√2/2, sin 60°=√3/2, sin 90°=1, showing a clear pattern for common angles.
How it works
cos values mirror sin values in reverse order: cos 0°=1, cos 30°=√3/2, cos 45°=√2/2, cos 60°=1/2, cos 90°=0.
Why it matters
tan values are calculated as sin/cos: tan 0°=0, tan 30°=1/√3, tan 45°=1, tan 60°=√3, and tan 90° is undefined.
Key detail
Memorising these standard values speeds up solving trigonometry problems without needing a calculator for common angles.
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Quick notes
• sin 0°=0, sin 30°=1/2, sin 45°=√2/2, sin 60°=√3/2, sin 90°=1.
• cos values mirror sin in reverse.
• cos 0°=1, cos 90°=0.
• tan = sin/cos.
• tan 45°=1, tan 90° is undefined.
• These are standard angle values.
• Memorising them speeds up problem-solving.
• They're used frequently without a calculator.