Assume a, b ∈ Z. Prove that if ax + by = 1 for some x, y ∈ Z, then gcd(a, b) = 1.

Prove the following statements
• corr(ax,y) = corr(x,y)
• show that if x,y and z are independent. Show what happened
to:
cov(x+y,x+z)= ?
• assume x and y are not independent:
cov(ax + b, y)= ?
70 tre la Car
Problem 11.21. For k є Z, we define Ak-{x є Z : x-51+ k for some 1 є z} (a) Prove that {Ak : k Z} partitions Z. (b) We denote by ~ the equivalence relation on Z that is obtained from the par- tition of part (a). Give as simple a description ofas possible; that is, given condition "C(x,y)" on x and y s x~y if and only if "C(x, y)" holds.
Problem 11.21. For k є Z, we...
X
and z are independent. Var(x)=1 ; Var(z) = sigma ^2. E(z)= 0 and y=
ax+b+z
I) cov(x,y)= ?
ii) corr(x,y)=?
dependent Varvane 2.
1. Let a, b,cE Z be positive integers. Prove or disprove each of the following (a) If b | c, then gcd(a, b) gcd(a, c). (b) If b c, then ged(a., b) < gcd(a, c)
Prove Valid: 1. (z)(Pz --> Qz) 2. (Ex) [(Oy • Py) --> (Qy • Ry)] 3. (x) (-Px v Ox) 4. (x) (Ox --> -Rx) ... :. (Ey) (-Py v -Oy) 1. (x) [(Fx v Hx) --> (Gx • Ax)] 2. -(x) (Ax • Gx) ..... :. (Ex) (-Hx v Ax) 1. (x) (Px --> [(Qx • Rx) v Sx)] 2. (y) [(Qy • Ry) --> - Py] 3. (x) (Tx --> -Sx) .... :. (y) (Py --> -Ty)
For constants a and b, X and Y are random variables. Please prove that, var(aX + bY ) = a 2 var(X) + b 2 var(Y ) + 2abcov(X, Y ) If X and Y are uncorrelated, what will be the results?
Prove that A = B for: A = {(x,y) e Rº : +y/<1} B = {(z,y) € RP: (71+ y)² < 1}
Let 1 ≤ m ∈ Z and let a,b ∈ Z be such that gcd(a,b) = m. Prove that gcd(a2,b2) = m2.
from the formula E(aX+b)=aE(x)+b, setting b = 0 we see that E(aX)= aE(X) Prove E(aX) = aE(x).
2. Prove the following useful properties of Dirac δ-functions (a) δ(ax) = (z) (b) zfic) =0 (c) f(x)5(-a) f(a)5(r d) δ(z-a (aメ0) a) ( dz9(x-a) ) where θ(x) is the step function defined as 1 if r 0 0 if r <0 θ(z) =
2. Prove the following useful properties of Dirac δ-functions (a) δ(ax) = (z) (b) zfic) =0 (c) f(x)5(-a) f(a)5(r d) δ(z-a (aメ0) a) ( dz9(x-a) ) where θ(x) is the step function defined as 1 if...