Question

What is the angle between the lines $x+y=1$ and $x-y=1$?

• A. $\frac{\pi }{6}$
• B. $\frac{\pi }{4}$
• C. $\frac{\pi }{3}$
• D. $\frac{\pi }{2}$

Answer 1

Answer: (D)

$\frac{\pi }{2}$

Given lines are $x+y=1$ and $x-y=1$

Slope of the first line is $m_1=-1/1=-1$

Slope of the second line is $m_2=-(-1)/1=1$

Let the angle between two lines is $\theta$ then

$\tan \theta =\frac{m_1-m_2}{1+m_1{m}_2}=\frac{1-(-1)}{1+1(-1)}=\infty$

Thus, the angle will be $\theta ={\tan }^{-1}\infty ={90}^o=\frac{\pi }{2}$