All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.

(i)

Equation of plane OABC: *r***a*** b*, for

Since

**is on plane OABC,**

*c*

**c**

**a***for are constants*

**b**(ii)

Using the ratio theorem formula,

(iii)

Area ONC = Area OMC

### KS Comments:

For (i), some students can rely on the law of parallelogram to show too. For (iii), students must know all their vector product manipulations well to do this.

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