2.2 Linear Transformation in Geometry Example. 1 Consider a linear ...

2.2 Linear Transformation in Geometry Example. 1 Consider a linear ... 2.2 Linear Transformation in Geometry Example. 1 Consider a linear ...

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Definition. orthogonal projection Let L be a line in R n consisting of all scalar multiples of some unit vector u. For any vector v in R n there is a unique vector w on L such that v − w is perpendicular to L, namely, w = (u·v)u. This vector w is called the orthogonal projection of v onto L: proj L(v) = (u · v)u The transformation proj L from R n to R n is linear. 8

Definition. Let L be a line in R n , the vector 2(proj Lv) − v is called the reflection of v in L: ref L(v) = 2(proj Lv) − v = 2(u · v)u − v where u is a unit vector on L. ✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏L ✏✏✏✶ ✏✏✏✏✏✏✏✏✏✏✶ projLv ✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✏✶ ❇▼ ❇ ❇ 2projLv ❇ ❇ ❇ ❇ ★ ❇ ★★★★★★★★❲ v ★ ★★★★★★★★❲ ✲ ✲ u refLv Homework. Exercise 2.2: 1, 9, 13, 17, 27 9

Def<strong>in</strong>ition. orthogonal projection Let L be<br />

a l<strong>in</strong>e <strong>in</strong> R n consist<strong>in</strong>g of all scalar multiples<br />

of some unit vector u. For any vector v <strong>in</strong> R n<br />

there is a unique vector w on L such that v − w<br />

is perpendicular to L, namely, w = (u·v)u. This<br />

vector w is called the orthogonal projection<br />

of v onto L:<br />

proj L(v) = (u · v)u<br />

The transformation proj L from R n to R n is l<strong>in</strong>ear.<br />

8

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