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Edexcel IGCSE Maths 復習筆記 4.9.1 SOHCAHTOA

Category: IGCSE課程, 國際課程, 教材筆記, 福利干貨 Date: 2022年6月28日下午6:47

Edexcel IGCSE Maths 復習筆記 4.9.1 SOHCAHTOA

What is SOHCAHTOA?

SOHCAHTOA is a mnemonic – ie a way to remember the 3 important formulas for sin (sine), cos (cosine), and tan (tangent)
In a right-angled triangle, label one angle (NOT the right angle!), and label the sides of the triangles as follows:

Right-Angled-Triangles-OAH-Theta

Note that:
θ?= Greek letter thetaO?= opposite

A?= adjacentH?= hypotenuse

'H' is always the same, but 'O' and 'A' depend on which angle we're calling θ
Using those labels, the three?SOHCAHTOA?equations are:

7.18.1-SOHCAHTOA-RN-1

Using SOHCAHTOA

Label the triangle: the angle you know (or want to know) is 'θ' -- 'O' and 'A' follow from thatChoose SOH, CAH, or TOA
The letters of the sides you're interested in (ie. know or want to know) tell you which to choose
To find a side: put and the side you know into the equation from 2, and solve to find the side you don't know
To find an angle: use the inverse trig functions on your calculator:

7.18.1-SOHCAHTOA-RN-2

Exam Tip

SOHCAHTOA (like Pythagoras) can only be used in right-angles triangles – for triangles that are not right-angled, you will need to use the Sine Rule or the Cosine Rule.Also, make sure your calculator is set to measure angles in degrees.