Math Is Fun Forum

mathisfun7

Member

Registered: 2015-11-14

Posts: 1

Help Please

2 questions, i know they have been answered before in other threads but i did not really understand those answers.

(1) Degrees are not the only units we use to measure angles. We also use radians. Just as there are 360 degrees in a circle, there are 2pi radians in a circle. Compute tan pi/3.

(2) In triangle GHI, we have GH = HI = 25 and GI = 30. What is sin GHI?

Thanks

Bob

Administrator

Registered: 2010-06-20

Posts: 10,163

Re: Help Please

hi mathisfun7

Welcome to the forum.

Q1. To change radians into degrees, divide by 2pi and times by 360.

http://www.mathsisfun.com/geometry/radians.html

If you start with an equilateral triangle with sides 2 and split it in two down a line of symmetry you make a triangle with angles 30-60-90 and  hypotenuse = 2 and adjacent (to 60) = 1.

By Pythagoras the opposite is  √3.

You should be able to finish this from here.

Although you could convert this to an approximate decimal it is usual to leave it with the root sign.

Q2.  You can make a right angled triangle out of GHI in the same way.  Then use Pythag. to get the height.

Several ways to finish this depending on how much trig. you know.

Simplest to find angle GHM where M is the midpoint of GI, then double it and use a calculator to get the sine.

But it comes out to be an exact fraction so a more advanced method is the write down fractions for sin(GHM) and cos(GHM) and then use the formula

http://www.mathsisfun.com/algebra/trigo … ities.html

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob