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:
- Note that:
θ = Greek letter theta
O = opposite
A = adjacent
H = 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:
- Label the triangle: the angle you know (or want to know) is ‘θ’ — ‘O’ and ‘A’ follow from that
Choose 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:
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.