Some concept about Vector

Answer should be √ (4^2 + 3^2) = 5. Is it right?

|OA| = 2 means length of A is 2
|OB| = 3 means length of B is 3

For |2OA + OB|, we join the 2 vectors A and 1 vector B to form a triangle.

Let length of |2OA + OB| = c,

Then, as a^2 + b^2 = c^2,
So, (2+2)^2 + 3^2 = c^2
i.e. c = √ (4^2 + 3^2) = 5

Vector, to a certain extent, is trigonometry matter.

Please comment.

因為直接計 2(2)+3=10, 條件是他們是相連的. 如果有夾角, 計出的長度便不同.
記住 vector 必須從立體考慮, 你可以試試真的劃個平行四邊形出來, 一條係oa+oa 咁長, 一係 OB 咁長, 但夾角係 120 度. 2OA + OB 就係這四邊形的對角線長度.