HELP FAST PLEASE!!Martin simplified the composed function f(x)=sin(arctan x). His work is shown below. Step 1: f(x)=sinA, where A=arctan x and x = tanAStep 2: tanA= opp/adj=x/1Step 3: hypotenuse= square root of 1^2-x^2= square root of 1-x^2Step 4: sinA=opp/hyp=x/squareroot 1-x^2In which step did Martin make is first error?

we have that

Step 1: f(x)=sinA, where A=arctan x and x = tanA-----> is correct
Step 2: tanA= opp/adj=x/1-----------> is correct
Step 3: hypotenuse= square root of 1²-x²= square root of 1-x²-----> is not correct
Because hypotenuse= square root of (1² + x²)=square root of (1+x²)
Step 4: sinA=opp/hyp=x/square root of (1+x²)

the answer is
In step 3 Martin make is first error