Let f(x)={ex−1x2−5x+6,x<0,x≥0 and g(x)=f(∣x∣)+∣f(x)∣. If the number of points where g is not continuous and is not differentiable are α and β respectively, then α+β is equal to ____
Answer: 4
Solution
Here f(x)=ex−1 for x<0 and f(x)=(x−2)(x−3) for x≥0. Since ∣x∣≥0 always, f(∣x∣)=∣x∣2−5∣x∣+6=x2−5∣x∣+6, which is continuous everywhere and differentiable except at x=0, where the −5∣x∣ term produces a corner. For ∣f(x)∣: at x=0, limx→0−f(x)=e−1=6=f(0), so f and hence ∣f(x)∣ has a jump at x=0; on x≥0, ∣(x−2)(x−3)∣ has corners at x=2 and x=3 where the product changes sign. Adding, g(x)=f(∣x∣)+∣f(x)∣ is discontinuous only at x=0, so α=1. It fails to be differentiable at x=0 (jump), x=2 and x=3, so β=3. Therefore α+β=4.