Let S={(a,b,c,d):a2 =b2 ,a,b,c,d∈R}. Is S a subspace of R4 ? If it is, justify why it is a subspace. If it is not, state a property it fails. 10. Let set S (a,b,c):5a−4b+7c=0,a,b,c∈R}. Is S a subspace of R3? If it is, justify why it is a subspace. If it is not, state a property it fails.