It is known that the first n terms and Sn of sequence {an} satisfy Sn = 2an-1, and the arithmetic sequence {BN} satisfies B1 = A1, B4 = 7. Find the general term formula of sequence {an}, {BN}

It is known that the first n terms and Sn of sequence {an} satisfy Sn = 2an-1, and the arithmetic sequence {BN} satisfies B1 = A1, B4 = 7. Find the general term formula of sequence {an}, {BN}

When ∵ Sn = 2an-1, ∵ n ≥ 2, sn-1 = 2an-1, ∵ an = 2an-1, n = 1, when an = 2an-1, ∵ an = 2an-1, n = 1, A1 = 2a1-1, ∵ A1 = 1, ∵ sequence {an} is a proportional sequence with 1 as the first term and 2 as the common ratio, ∵ an = 2N-1; ∵ B1 = A1, B4 = 7, ∵ B1 = 1, tolerance 2, ∵ BN = 1 + (n-1

Let P = (a + C, b) and q = (B − a, C − a). If P ‖ Q, then the size of angle c is______ ．

Because P ∥ Q, a + CB − a = BC − a, B2 AB = c2-a2, that is, A2 + b2-c2 = ab. by cosine theorem COSC = A2 + B2 − c22ab = 12, C = π 3, so the answer is: π 3

Let P = (a + C, b), q = (B, C-A). If P ∥ Q, then the size of angle C

Obviously, P and Q are not zero vectors
therefore
b/(a+c)=(c-a)/b
So C ^ 2 = a ^ 2 + B ^ 2
∠C=90°

Let P = (a + C, b) and q = (B − a, C − a). If P ‖ Q, then the size of angle c is______ ．

Because P ∥ Q, a + CB − a = BC − a, B2 AB = c2-a2, that is, A2 + b2-c2 = ab. by cosine theorem COSC = A2 + B2 − c22ab = 12, C = π 3, so the answer is: π 3