Grade five, CIE IGCSE Maths

Revision Notes

What is SOHCAHTOA?

Some American maths teachers claim (jokingly) that Sohcahtoa was a great Native American chieftain and mathematician.  In fact SOHCAHTOA is a mnemonic – ie a way to remember the three 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, IGCSE & GCSE Maths revision notes

(∅  is the Greek letter theta.  ‘O’ stands for opposite, ‘A’ for adjacent, and ‘H’ for hypotenuse.  ‘H’ is always the same, but ‘O’ and ‘A’ depend on which angle we’re calling ∅!)

Sohcahtoa equation, IGCSE & GCSE Maths revision notes

Using SOHCAHTOA

  1. Label the triangle.  The angle you know (or want to know) is ‘‘∅’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.
  2. 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.
  3. To find an angle, use the inverse trig functions on your calculator:

Sohcahtoa equation 2, IGCSE & GCSE Maths revision notes

Example

SOHCAHTOA Example 1, IGCSE & GCSE Maths revision notes
Two Right Angled Triangles with measurements, IGCSE & GCSE Maths revision notes
SOHCAHTOA Example 2, IGCSE & GCSE Maths revision notes
Right Pointing Right Angled Triangle with measurements, IGCSE & GCSE Maths revision notes
SOHCAHTOA Example 3, IGCSE & GCSE Maths revision notes
Left Pointing Right Angled Triangle with measurements, IGCSE & GCSE Maths revision notes
SOHCAHTOA Example 4, IGCSE & GCSE Maths revision notes

Question

Edexcel GCSE Maths Notes

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