the greatest and the least resultant of 2 forces acting at a point is 10newton and 6newton respectively.
if each force is increased by 3newton, find the resultant of new forces when acting at a point at an angle of 90degree with each other.

Let, 1st force = a

2nd force = b

A.T.Q,

a+b = 10

a-b = 6

Calculate for a & b, you'll get a=8 & b= 2

After increasing by 3, it'll be a = 8+3 = 11 & b=2+3 = 5

Resultant force at 90 degree angle = 11+5 = 16 Newtons

The solution would be like this for this specific problem:

if resultant of new forces when acting at a point at an angle of 90Degrees with each other:
(x^2+y^2+2xycos90*)^1/2
=(121+25)^1/2
=146^1/2
=12.08N

I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.

newton's first law of motion