a.) t0 = 1
[f(t)- f(t0)] / [ t - t0 ] =
[√(4t) - √ (4*1)] / [t - 1] =
[ √(4t) - √(4)] / [ t - 1] =
[ 2 √(t) - 2] / [t - 1] =
2 [√(t) - 1] / [t - 1] =
2[√(t) - 1] / [ (√(t) - 1) (√(t) + 1) ] =
2 / (√(t) + 1)
b.) t0= 4
[√(4t) - √ (4*4)] / [t - 4] =
[ √(4t) - √(16)] / [ t - 4] =
[ 2 √(t) - 4 / [t - 4] =
2 [√(t) - 2] / [t - 4] =
2 [√(t) - 2] / [ (√(t) - 2) (√(t) + 2) ] =
2 / (√(t) + 2)