For planes x+11y+2z=5 and 2x+y+11z=7, what is cos theta between them?

A. 35 / 126

Step 1: the angle between planes is the angle between their normal vectors. Step 2: normals are (1,11,2) and (2,1,11); dot=35 and both magnitude squares are 126, so cosθ=35/126. Step 3: tip: use plane coefficients as normal vectors.

Step 1: planes का angle उनके normal vectors के angle जैसा होता है। Step 2: normals (1,11,2) और (2,1,11) हैं; dot=35 और दोनों magnitude square 126 है, इसलिए cosθ=35/126। Step 3: tip: plane angle में coefficients को normal vector मानें।