By definition of tangent,
tan(<em>x</em>) = sin(<em>x</em>) / cos(<em>x</em>)
so if tan(<em>x</em>) < 0, and we're given cos(<em>x</em>) = -1/4 < 0, then it follows that sin(<em>x</em>) > 0.
Recall the Pythagorean identity:
cos²(<em>x</em>) + sin²(<em>x</em>) = 1 → sin(<em>x</em>) = + √(1 - cos²(<em>x</em>))
Then
sin(<em>x</em>) = √(1 - (-1/4)²) = √(15/16) = √(15)/4
Recall the double angle identity:
sin(2<em>x</em>) = 2 sin(<em>x</em>) cos(<em>x</em>)
Then
sin(2<em>x</em>) = 2 • √(15)/4 • (-1/4) = -2√(15)/16 = -√(15)/8
That would be all numbers equal or greater than -3.
Thats the last choice.
Note the solid dot means that -3 is included in the domain
3*|2-7| = 3*|-5|......absolute values are positive even when they say negative.
so 3*| -5 | = 3 * 5 = 15
