5th question Q 5 The quadratic expression 21+12x-4x2 takes (a) the least value 5 (b) the highest value 30 - Maths - Differential Equations

Question

5th question
Q 5 The quadratic expression 21 + 12 x - 4 x 2 takes
(a) the least value 5
(b) the highest value 30
(c) the highest value 21
(d) none of these

Brijendra Pal · Accepted Answer

Hi, 21+12x-4x2=21-4x2-3x=21-4x2-3x+322-322=21-4x2-3x+322-94=21-4x-322-94=21+9-4x-322= 30-4x-322Now x-322, being a square quantity ≥0 so maximum value of 30-4x-322 will be at x-322= 0 so maximum value = 30

5th question Q.5. The quadratic expression 21 + 12 x - 4 x 2 takes (a) the least value 5 (b) the highest value 30 (c) the highest value 21 (d) none of these

5th question
Q.5. The quadratic expression $21 + 12 x - 4 x^{2}$ takes
(a) the least value 5
(b) the highest value 30
(c) the highest value 21
(d) none of these