Find the gradient of the curve y = x² + 3x at x = 2.
A5
B7CORRECT
C10
D12
AI
Toasta AI Explanation
Why the answer is B, and why the others tempt you.
**The reasoning**
The gradient of a curve at any point is found using **differentiation**. When you differentiate, you're finding how steep the curve is at that exact spot.
Given: y = x² + 3x
**Step 1:** Differentiate using the power rule (bring down the power, reduce the power by 1):
- dy/dx = 2x + 3
**Step 2:** Substitute x = 2:
- dy/dx = 2(2) + 3 = 4 + 3 = **7**
That's your gradient at x = 2.
**Why the wrong options tempt you**
- **Option A (5):** You likely forgot to multiply the 2 in front of x, doing just 2 + 3 instead of 2(2) + 3.
- **Option C (10):** You probably found y itself at x = 2 (which is 4 + 6 = 10) instead of finding dy/dx. Remember: gradient ≠ y-value!
- **Option D (12):** Maybe you multiplied 2 × 2 × 3 incorrectly or confused the operations.
**Quick takeaway**
Gradient = differentiate first, then substitute the x-value — never substitute before differentiating!
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