Find the product of (a+2b) and (a−2b).
a2+4b2
a2−4b2
−a2+4b2
−a2−4b2
(a+2b)(a−2b) ⇒a(a−2b)+2b(a−2b) ⇒a2−2ab+2ba−4b2
⇒a2−2ab+2ab−4b2
⇒a2−4b2
If a-2b = 15 and find a2+ 4b2 .
If a2+4b2=12ab, then log (a + 2b) is