Answer:
1
Step-by-step explanation:
[tex]cos²30° + cos²60° + cos²90°\\ + 2 cos 30° cos 60° cos 90° \\ \\ = \bigg( \frac{ \sqrt{3} }{2} \bigg) ^{2} + \bigg( \frac{ 1 }{2} \bigg) ^{2} + \bigg( 0\bigg) ^{2} \\ + 2 \times \frac{ \sqrt{3} }{2} \times \frac{ 1 }{2} \times 0 \\ \\ = \frac{3}{4} + \frac{1}{4} + 0 + 0 \\ \\ = \frac{3 + 1}{4} \\ \\ = \frac{4}{4} \\ \\ = 1[/tex]
