Exercise 1: Computing dL/dz2 — Possible Solution
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GIVEN
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L = (z2 - y_target)^2
z2 = -0.2769, y_target = 1.0

STEP 1: APPLY THE CHAIN RULE TO THE SQUARED-ERROR LOSS
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L is itself a composed function: an outer function u^2 wrapped
around an inner function u = z2 - y_target.

d/du[u^2] = 2u (power rule)
du/dz2 = 1 (since y_target is a constant, d/dz2[z2-y_target] = 1)

dL/dz2 = 2u * 1 = 2(z2 - y_target)

STEP 2: SUBSTITUTE THE ACTUAL VALUES
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dL/dz2 = 2 * (-0.2769 - 1.0) = 2 * (-1.2769) = -2.5538

RESULT
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dL/dz2 = -2.5538 (matching this chapter's own stated value exactly)

WHY THIS WORKS AS AN ANSWER
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The squared-error loss is explicitly recognized as a composed
function (outer square, inner subtraction) before applying the
chain rule, rather than just quoting the "2(z2-y)" formula as a
memorized fact, and the numeric substitution is shown as its own
explicit step.