Question

Please help! a=22, b=10, C=70 degrees.
A=?

Answer 1

sounds like cosine law :/

Answer 2

Here, you have ONE angle and two adjacent sides: perfect condition for the cosine law, as Igbasallote suggested.

Answer 3

use sin law
\[\Large \frac{a}{\sin(A)}=\frac{b}{\sin(B)}=\frac{c}{\sin(C)}\]

Answer 4

Please elaborate.

Answer 5

you can find c in the above using cosine Law
\[\Huge c^2=a^2+b^2-2abcos(C)\]

Answer 6

Whew!

Answer 7

Can you go step by step with me on this one? I don't understand :/

Answer 8

Yes, in fact, we need to use the sine law to find A.

Answer 9

But that would be after we have found c

Answer 10

using the cosine law.

Answer 11

ok using the above cosine Law
\[\Large c^2=a^2+b^2-2abcos(C)\]
\[\Large c^2=(22)^2+(10)^2-2(22)(10)\cos(70)\]
tell me the value of c now.use your calculator.

Answer 12

c^2=433.511

Answer 13

yes

Answer 14

take square root

Answer 15

20.82

Answer 16

yes

Answer 17

now using the above sin law
\[\Large \frac{a}{\sin(A)}=\frac{c}{\sin(C)}\]
\[\Large \frac{22}{\sin(A)}=\frac{20.8}{\sin(70)}\]
can you find A now ???

Answer 18

20.8/sin(70)=22.13

Answer 19

nopes!
\[\Large \sin(A)=\frac{22*\sin(70)}{20.8}\]
first solve the right side then take the sin inverse to Get A.

Answer 20

Sorry, OS crashed on me. O.k. So I got .9939 and then took sin inverse which gave me 83.66

Answer 21

yes that's correct !!!!!!!

Answer 22

Thank you so much! I appreciate your teaching :)

Answer 23

you are welcome :)
any way it is really hard to get these A's everywhere (specially in Exams) :P

Answer 24

Yes, it kinda is. Especially since math is my worst subject of all time! Can I ask you a question? What's the meaning of your pic? Is that your baby?