If (x – a)2 + (y – b)2 = c2, for some c > 0, prove that
3
2
2
2
2
1
dy
dx
d y
dx




+







is a constant independent of a and b 16 If cos y = x cos (a + y), with cos a ≠ ± 1, prove that 
cos (2
)
sin
dy
a
y
dx
+a
= 17