Monday

September 22, 2014

September 22, 2014

Posted by **Rose** on Sunday, April 14, 2013 at 8:23am.

what is the measure of angle ABC

I plotted it on a gragh and got

1.46 degress. I am unsure if I am doing this question correctly. Or am I misreading it

thanks in advance .

- math -
**Reiny**, Sunday, April 14, 2013 at 10:12amA simple sketch will show you that that answer cannot possibly be right

Extend CB to cut the x-axis at D

(using the basic concept that if the slope of a line is m and the line forms an angle of Ø with the x-axis

then tanØ = m)

slope of AB = 1/3

so tan BAD = 1/3

BAD = 18.43°

slope of CB = -3/2 , angle is obtuse

tan (angle of line with x-axis) = 123.69°

so angle BDA = 56.304°

and angle ABC is the exterior angle

and angle ABC = angle BAD + angle BDA

= 18.43° + 56.304° = 74.74°

or

If you know vectors

vector CB = (-2,3)

vector BA = (-3,-1)

v(CB) ∙ v(BA) = |CB||BA)cosØ, where Ø is our angle

6 - 3 = √13 √10 cos‚

cosØ = 3/√130 = .26311..

Ø = 74.74° as above.

**Answer this Question**

**Related Questions**

Math - Given the points A(0,0)B(3,1), and C(1,4), what is the measure of angle ...

Math - Given the points A(0,0),B(3,1),and C(1,4), what is the measure of angle ...

Geometry - Angle ABC and ange DBE are vertical angles,the measure of angle ABC...

Geometry - Angle ABC and ange DBE are vertical angles,the measure of angle ABC...

help math - In triangle ABC, points D,E,F are on sides BC,CA,AB respectively ...

Geometry - ABC is an acute angle triangle with points D and E on BC and AC, ...

Geometry - ABC is an acute angle triangle with points D and E on BC and AC, ...

Math - Given the points A(0,0), B(4, 3) and C(2,9), what is the measure of angle...

Geometry - Given: in triangle ABC, angle B= 120 degrees Prove: angle A does not...

Math - 1. Find the angle of smallest positive measure coterminal with an angle ...