9-1 SOHCAHTOA

SOHCAHTOA

- sinθ= oppisite/hypotenuse

- cosθ= adjacent/hypotenuse

- tanθ= oppisite/adjacent

-Only use on right triangles

-You can’t use the 90º angle

-An angle of elevation

-Angle of depression

Since Brob loves word problems there will be A LOT of those on the test. Woohoo.

Example 1: In triangle ABC, angle A is 90º, angle B is 25º, leg a is 18. Find b and c.

You start off my drawing what you know, and then you look at your formulas and see which one you can use to solve the rest of the triangle. The only angle you can use is B because you can’t use your 90º.

We’re going to solve for leg b first. 25º is opposite of leg b and the only other number you have to work with is 18 so you look at your formula and sinθ=opp. over hyp.

sin25º=b over 18 (cross multiply)

(plug into your calculator) 18sin25 would give you around 7.607

Now we’re going to find leg c. Using angle B again, c is adjacent to angle B and using the only other number you have 18 you would use the formula cosθ=adj. over hyp.

cos25º=c over 18 (cross multiply)

(plug into calculator) 18cos25 this would give you around 16.314

Just to finish off the triangle to find angle C you would add 90º+25º-180º=65º

Now fill in the rest of the triangle.

I tried to draw a picture and it didn't work because blogger hates me :(

--Danielle