Answer : Option A
Explanation:
we can clearly see that from x+ y=5 we can substitute y = 5-x in y = 9x^2
Option B is clearly incorrect x can not be y -5
Option C is incorrect because y can not be 5 +x
Option D is incorrect because its y = 9x^2 not y^2 =9x^2 so y can not be 3x
if its y^2 = 9x^2 then only implies y = 3x
So for the first one what you did was wrong as in wrong formula.
Radius is 5cm as it is given and diameter is double the radius which is 10.
So r=5
And D=10.
For the second one the diameter is 16cm as it is given and radius is half the diameter,so half of 16 is 8cm right?
So r=8
And D=16
