Precalculus, Chapter 10, 10.1, Section 10.1, Problem 49

Given:
x-2y=7
6x+2y=5

Find the slope for line 1.
x-2y=7
-2y=-x+7
y=1/2x-7/2
The slope of line 1 is m_1=1/2.

Find the slope of line 2.
6x+2y=5
2y=-6x+5
y=-3x+5/2
The slope line 2 is m_2=-3.

Find the slope between two lines using the formula
tan(theta)=|(m_2-m_1)/(1+m_1m_2)|

tan(theta)=|((-3)-(1/2))/(1+(1/2)(-3))|=7

theta=arctan(7)=81.9^@=1.4289 radians

The angle between the two lines is 81.9 degrees or 1.4289 radians.