jika f(x)= a tan x + bx, f'(pi/4) = 3, dan f'(pi/3) = 9, maka a+b =...

f'(x) = a sec²x + b
f'(pi/4) = a sec²(45°) + b = 3
f'(pi/3) = a sec²(60°) + b = 9
-------------------------------------- -
a sec²(45) - a sec²(60) = -6
a(2/√2)² - 2²) = -6
a(2 - 4) = -6
a = -4, masukan pada salahsatu
-4(2²) + b = 9
b = 25
a + b = -4 + 25 = 21