已知:实常数a、b、c、d同时满足下列两个等式:①asinθ+bcosθ﹣c=0;②acosθ﹣bsinθ+d=0(其中θ为任意锐角),则a、b、c、d之间的关系式是:____
To ______ something to happen means to believe that it will happen.