Q. Show that H=(x,y,z)∈R3∣x+2y=0 is a subspace of R3.
Check zero vector: To determine if H is a subspace of R3, we need to check if it satisfies three properties: it must contain the zero vector, it must be closed under vector addition, and it must be closed under scalar multiplication.
Verify vector addition closure: First, we check if H contains the zero vector. The zero vector in R3 is (0,0,0). If we substitute x=0 and y=0 into the equation x+2y=0, we get 0+2(0)=0, which is true.
Confirm scalar multiplication closure: Second, we check if H is closed under vector addition. Take any two vectors(x1,y1,z1) and (x2,y2,z2) in H. According to the definition of H, we have x1+2y1=0 and x2+2y2=0. We need to check if their sum (x1+x2,y1+y2,z1+z2) is also in H. We calculate (x1+x2)+2(y1+y2)=(x1+2y1)+(x2+2y2)=0+0=0, which means the sum is also in H.
Confirm scalar multiplication closure: Second, we check if H is closed under vector addition. Take any two vectors (x1,y1,z1) and (x2,y2,z2) in H. According to the definition of H, we have x1+2y1=0 and x2+2y2=0. We need to check if their sum (x1+x2,y1+y2,z1+z2) is also in H. We calculate (x1+x2)+2(y1+y2)=(x1+2y1)+(x2+2y2)=0+0=0, which means the sum is also in H.Third, we check if H is closed under scalar multiplication. Take any vector (x1,y1,z1)2 in H and any scalar (x1,y1,z1)4. According to the definition of H, we have (x1,y1,z1)6. We need to check if (x1,y1,z1)7 is also in H. We calculate (x1,y1,z1)9, which means the scalar multiple is also in H.