How to ask for input after if statement comes true in python [closed]

I am beginner in python I was recently coding I wanted to user to input after the if statement comes true but I doesn't seem to work please help me

op = input("enter operation  ",)
if op == 'area'
shape = input ('enter shape ',)
if shape ==' tri' :
print ("the area of triangle ",1/2*n*v)