backprop

9 problems

• Conv2D backward (dx, dW)Hard
• ReLU forward + backwardEasy
• Sigmoid forward + backwardEasy
• MSE loss + backwardEasy
• Linear backward (chain rule)Medium
• Cross-entropy gradientMedium
• GELU backward (tanh approximation)Medium
• Matmul backwardMedium
• Softmax backwardMedium