Question

If the angle between a and c is $25{}^{\circ },$ the angle between b and c is $65{}^{\circ },$ and $a+b=c,$ then the angle between a and b is

• A. $40{}^{\circ }$
• B. $115{}^{\circ }$
• C. $25{}^{\circ }$
• D. $65{}^{\circ }$
• E. $90{}^{\circ }$

Answer 1

Answer: (E)

Let the angle between a and c is $\theta$ , then $\theta =25{}^{\circ }$ and the angle between b and c is $\alpha$ , then $\alpha =65{}^{\circ }$ . $a+b=c$ ...(i) So, by parallelograms property
Resultant of a and $b=a+b=c$ [from Eq. (i)] So, angle between a and $b=25{}^{\circ }+65{}^{\circ }=90{}^{\circ }$