AP EAMCET Engineering 20 Apr 2019 Shift 1 Paper

Consider given points,
A(2,3,5),B(α,3,3),C(7,5,β)
The mid-point of BC is,
D(‌

α+7

2

,4,‌

3+β

2

)
The direction ratios of the lines joining the points A and D is,
(‌

α+3

2

,1,‌

β−7

2

)
The line axed AD is equally inclined with coordinate axis is,
‌

α+3

2

=1=‌

β−7

2

This implies,
α=−1 and β=9
So
cos−1(‌

α

β

)=Cos−1(−‌

1

9

)