a) Let u=(2,3,-1) and w=(3,-1,p). Given that u is perpendicular to w, find the value of p. b)Let v=(1,q,5). Given that modulus v = sqrt(42), find the possible values of q.

a) u is perpendicular to w, so u • w =0. This means that 23 + 3(-1) + (-1)*p = 0, so 6-3-p=0, hence p=3. b) The magnitude of v = sqrt(1²+q²+5²) = sqrt(42). Thus, 1+q²+25 = 42, q²=16, so q is either 4 or -4.