PLZ Help!!!!!!!!!!!!?

Question

If a triangle ABC , AB=10, BC= 7 and AC=12. What is the measure of angle A to the nearest degrees?

Answer 1

use cosine law (because you don't know any of the angles)

---- cosine law used when you know the measurement of an angle between 2 known sides or when there're no known angles at all

a^2= b^2 + c^2 - 2bc x cosA

b^2= a^2 + c^2 - 2ac x cosB

c^2= a^2 + b^2 - 2ab x cosC

c is side opposite angle C, a the side opp angle A, b the side opp angle B.

you first have to draw the triangle

after drawing it, you will see that the side opp angle A is BC, and it is 7 units long (label the sides as a, b, or c if that helps you). what you do afterwards is put the values into the equation.

(7)^2= (12)^2 +(10)^2 - 2(12)(10)cosA

isolate the unknown value

49 - 144 = 100 - 2(12)(10)cosA
-95-100 = -2(12)(10)cosA
-195 = -2(12)(10)cosA
-195/(-2 x 12 x 10) = cosA
cosA = 0.8125

to find A, just press cos^-1 0.8125 on your calculator.

angle A = cos^-1 0.8125
angle A = 35.65908.... degrees

rounded to nearest degree, angle A is 36 degrees

hope that helped :)

Answer 2

One way (probably the easiest way) to solve this problem is by using the Law of Cosines. The Law of Cosines states that:

a² = b² + c² - 2bc*cos(A)
b² = a² + c² - 2ac*cos(B)
c² = a² + b² - 2ab*cos(C)

Now, don't get confused because there are three formulas. They are simply three different versions of the SAME formula. You just switch the letters in the formula around, based on which angle you would like to solve for.

OK, now that the fundamentals are out of the way, let's go ahead and try to solve your problem...

We're trying to solve for angle A here. Now, according to the Law of Cosines formula, the sides are a, b, and c. But in your problem, the sides are AB, BC, and AC. Let's rewrite the formula in terms of these to make the problem less confusing!:

BC² = AB² + AC² - 2(AB)(AC)cos(A)

That's it!!! Now all you have to do is plug in the numbers that you know, and solve for angle A!!!:

7² = 10² + 12² - 2(10)(12)cos(A)
49 = 100 +144 - 240cos(A)
49 = 244 - 240cos(A)
-195 = -240cos(A)
.8125 = cos(A)
cos˙¹ (.8125) = A
A = ~35.6591

There ya go! Angle A is approximately 35.6591.
I hope I helped ya! If there's anything that you don't quite understand about my explanation, send an e-mail my way and I'll do my best to clarify. :)

Answer 3

You can find the angle by equalling the sine of A to 7/12 (opposite over hypotenuse); you should have a calculator that can take the arcsin(7/12). This comes out to 35.68 degrees, or just 36.

Answer 4

do law of cosines......If you don't know how, this is the formula

7^2= 12^2 + 10^2 - 2(10)(12)cosx

49= 144+100-240cosx
49=244-240cosx
-195=-240cosx
-195/-240 = cos x
cosx =.8125
x=36.6590877 or 37 degrees

Answer 5

7^2 = 10^2 +12^2 - 2(7)(cosA)
49 = 100 + 144 - 14cosA
49 = 244 - 14cosA
-195 = - 14cosA
195/14 = cosA
THERE IS NO ANSWER/EMPTY SET BECAUSE COSINE OF ANY NUMBER CAN'T BE MORE THAN ONE

Answer 6

i think u gotta use the Cosine Law for that... but i'm not sure i remember it. i think i learnt it when i was in school... we use one of the laws of triangles...





























u NEED tuitions dude,,, what are u doing over here... ??? this is the wrong place!

Answer 7

Hi 45o as near as I can work it out

Answer 8

Either it's ur first day of geometry or you are going to fail that class....