for 3:
tan = sin/cos
cos²(y) + sin²(y) = 1
letting y = arcsin(x), sin²(y) = sin²(arcsin(x)) = x²
cos(arcsin(x)) = sqrt(1-x²)
therefore,
tan(arcsin(x)) = x/cos(arcsin(x)) = x/sqrt(1-x²)
for 6:
for x > 0, |x²sin(1/x)| >= 0
also, for y > 0, |sin(y)| <= 1
letting y = 1/x, |sin(1/x)| <= 1
that is : x²*1 >= |x²sin(1/x)| >= 0 i.e x² >= |x²sin(1/x)| >= 0
lim x² = 0 = lim 0, squeeze rule applies : lim |x²sin(1/x)| = 0 therefore lim x²sin(1/x) = 0