Martin simplified the composed function \( f(x)=\sin (\arctan x) \). His work is shown below. Step 1: \( f(x)=\sin A \), where \( A=\arctan x \) and \( x=\tan A \) Step 2: \( \tan A=\frac{\text { opposite }}{\text { adjacent }}=\frac{x}{1} \) Step 3: hypotenuse \( =\sqrt{1^{2}-x^{2}}=\sqrt{1-x^{2}} \) Step 4: \( \sin A=\frac{\text { opposite }}{\text { hypotenuse }}=\frac{x}{\sqrt{1-x^{2}}} \) In which step did Martin make his first error? (1 point) step 1 step 2 step 3 step 4 He did not make an error.

Let's review Martin’s work: 1. In Step 1, Martin correctly writes: f(x) = sin(arctan x), letting A = arctan x, so that x = tan A. 2. In Step 2, he correctly sets up a right triangle with opposite side = x and adjacent side = 1 since tan A = x/1. 3. In Step 3, he calculates the hypotenuse. However, using the Pythagorean theorem, the hypotenuse should be √(1² + x²) = √(1 + x²), not √(1 - x²). 4. Step 4 then uses the incorrect hypotenuse, yielding an incorrect expression. Thus, the first error is in Step 3.