# some one check my trig!!

Printable View

• Aug 6th 2010, 11:51 AM
gabriel
some one check my trig!!
so there's a right triangle
90 degrees in the bottom left
30 degrees bottom right
15 in length
unknown adjacent
unknown hypotenuse
so i did sin(30) = 15/b
15/sin(30)=30=b
and did tangent(30)=15/a
15 * tan(30)= 8.66=a
is this correct?
• Aug 6th 2010, 11:58 AM
Ackbeet
What is your "15 in length"? What does that correspond to? The length of the side opposite to the 30 degrees? What is b? The hypotenuse? What is a? The side adjacent to the 30 degrees?
• Aug 6th 2010, 12:36 PM
Archie Meade
Quote:

Originally Posted by gabriel
so there's a right triangle
90 degrees in the bottom left
30 degrees bottom right
vertical side is 15 in length
unknown adjacent to the 30 degree angle
unknown hypotenuse

so i did sin(30) = 15/b....

correct

15/sin(30)=30=b....correct

and did tangent(30)=15/a...correct

15 * tan(30)= 8.66=a... incorrect

is this correct?

Using tangent, you have 2 ways to find "a"

$tan30^o=\frac{15}{a}$

$\frac{tan30^o}{1}=\frac{15}{a}$

$\frac{1}{tan30^o}=\frac{a}{15}$

Now multiply both sides by 15.

Or....

$tan30^o=\frac{15}{a}$

first multiply both sides by "a"

$atan30^o=\frac{15a}{a}=15$

Finally divide both sides by $tan30^o$ to get "a".

Notice from your diagram that "a" should certainly be longer than 15 units.
• Aug 6th 2010, 12:42 PM
gabriel
so 15/tan(30) = 25.98 app. 26 is this the final correct answer for a?
• Aug 6th 2010, 12:52 PM
Archie Meade
Quote:

Originally Posted by gabriel
so 15/tan(30) = 25.98 app. 26 is this the final correct answer for a?

Yes,
but you need to be "correct" on the technique!
When you are, you will get very used to having correct answers.