## britbrat4290 Group Title Solve the triangle. Round lengths to the nearest tenth and angle measures to the nearest degree. a = 7, b = 7, c = 5 11 months ago 11 months ago

1. britbrat4290 Group Title

B. A = 69°, B = 69°, C = 42°??

2. mebs Group Title

sounds good.

3. britbrat4290 Group Title

wrong

4. mebs Group Title

Try Using cosine law

5. mebs Group Title

$7^{2} = 7^{2} + 5^{2} - 2(7)(5)cosA$

6. britbrat4290 Group Title

my answers need to be in degrees

7. mebs Group Title

you get $cosA = \frac{ -25 }{ -70 }$ than do arc cosine. you get angle 69.07

8. britbrat4290 Group Title

i need degrees for a b n c ??

9. mebs Group Title

you get angles 41.8 and 69.07. again

10. britbrat4290 Group Title

A. A = 70°, B = 70°, C = 40° B. A = 69°, B = 69°, C = 42° C. A = 42°, B = 69°, C = 69° D. A = 69°, B = 42°, C = 69°

11. mebs Group Title

|dw:1375984676609:dw| ?

12. mebs Group Title

Try D.

13. mebs Group Title

have to go.

14. britbrat4290 Group Title

thanks

15. britbrat4290 Group Title

deff not 69 deg

16. genius12 Group Title

Note that the triangle is isosceles:|dw:1375984026354:dw|

17. britbrat4290 Group Title

ok ? still confused

18. genius12 Group Title

Now use the cosine law:$\bf a^2=b^2+c^2-2bc \cos(A) \implies 5^2=7^2+7^2-2(7)(7)\cos(A)$Note that 'A' is the angle opposite side BC. Now re-arrange and solve for cos(A):$\bf \implies \cos(A)=\frac{-73}{-98}=0.7445 \implies \cos^{-1}(0.7445)=A=41.884 \ degrees$

19. genius12 Group Title

Now because the triangle is isosceles, the remaining two angles B and C are equal so we can find each of them by subtracting A from 180 and dividing the result by 2:$\bf \angle B=\angle C=\frac{ 180 -41.884}{ 2 }=69.058 degrees$Rounding off our results to the nearest degree we get:$\bf \angle A =42 \ degrees$$\bf \angle B=\angle C=69 \ degrees$ @britbrat4290

20. genius12 Group Title