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Showing 2 questions for Class 10. Tap a card to reveal the answer.
MathematicsIntroduction to TrigonometrymediumIf sin(theta) = 3/5, find cos(theta) and tan(theta), where theta is acute.
Reveal answer ↓
What it is
The identity sin^2 + cos^2 = 1 lets you find one trig ratio from another for the same angle.
Answer
Using the identity sin^2(theta) + cos^2(theta) = 1, cos^2(theta) = 1 - (3/5)^2 = 1 - 9/25 = 16/25, so cos(theta) = 4/5 (positive since theta is acute). Then tan(theta) = sin/cos = (3/5) / (4/5) = 3/4.
sin^2(theta) + cos^2(theta) = 1 ; tan = sin/cos
- •sin^2 + cos^2 = 1
- •cos(theta) = 4/5
- •tan(theta) = sin/cos = 3/4
Why learn this
Trig ratios drive navigation, physics waves, construction and computer graphics.
💡 Memory trick
Think of the 3-4-5 triangle: sin 3/5 -> cos 4/5 -> tan 3/4.
MathematicsIntroduction to TrigonometrymediumEvaluate 2 tan^2(45 degrees) + cos^2(30 degrees) - sin^2(60 degrees).
Reveal answer ↓
What it is
The standard angles 0, 30, 45, 60 and 90 degrees have fixed trig values worth memorising.
Answer
Use standard values: tan(45 deg) = 1, cos(30 deg) = sqrt(3)/2, sin(60 deg) = sqrt(3)/2. So the expression = 2(1)^2 + (sqrt(3)/2)^2 - (sqrt(3)/2)^2 = 2 + 3/4 - 3/4 = 2.
tan45 = 1 ; cos30 = sqrt(3)/2 ; sin60 = sqrt(3)/2
- •tan45 = 1, cos30 = sin60 = sqrt(3)/2
- •2(1) + 3/4 - 3/4
- •= 2
Why learn this
They appear in nearly every physics and maths problem - knowing them saves huge time.
💡 Memory trick
For sin, use sqrt(0..4)/2 across 0,30,45,60,90; cos is the same list reversed.