Question

construct the E,F,G if its perimeyer is 9cm and angle F and angle G is 90 degree

Answer 1

its not possible because in a triangle 2 angles could not be 90 degree. Please check your question before asking it.

Answer 2

it is not possible to draw the triangle you want
because have given that angle F and G both are of 90°
by angle sum property of triangle sum of all angles is 180°
you said two sides are of 90°
so
angle 1 + angle 2+ angle 3=180°
90+90+angle 3=180°
angle 3=0!!
here is the problem
any angle in triangle can't be zero

therefore the triangle can't be construed